Patricia Morales, Patricia García Herrera, Maria Cruz Matallana González, Montaña Cámara Hurtado, and Maria de Cortes Sánchez Mata
Department of Nutrition and Bromatology II, Faculty of Pharmacy, Complutense University of Madrid, Spain
The use of edible greens as food is as old as civilization. In the past, most people living in rural communities knew about a wide variety of wild plants that they used for many purposes, often linked to survival (food or medicinal uses; see Chapter 6). Many wild plants have been eaten and knowledge of how to identify them, the optimal moment of consumption, methods of preparation, and their uses was acquired by trial and error, and passed down through the centuries.
Agricultural activities have lead to a loss of diversity of plants consumed, and in the last century drastic changes in life styles (migrations, changes in food habit, etc.) have also lead to the loss of a vast part of this age‐old knowledge. Since the 20th century, some efforts have been made to recover it: scientists started to study the potential of wild plants as sources of nutrients as well as active principles for medicinal use; renewed interest in a lifestyle more integrated with nature has arisen in some parts of society; ethnobotanists and ethnozoologists have worked on compilation of traditional knowledge about the use of natural resources. In this context, some governments and international organizations (such as UNESCO or the World Intellectual Property Organization), perceiving the importance of preserving this richness, have funded some of these initiatives, and many strategies have been followed in order to revalorize the nutritional potential of wild edibles for improving the quality of modern diets. Knowledge of the nutrients and bioactive compounds in these traditionally used plants is a key point, which is currently gaining importance in the field of food chemistry.
The African continent has a special profile when compared to other world areas in terms of the state of knowledge about wild edible greens composition. The geographical situation of this continent with respect to the equator is reflected in its climatic zonation: from the Mediterranean regions of the North, through subtropical, tropical, and again subtropical areas in South Africa. This area includes many different types of ecosystems such as forests, savannahs, jungles, and deserts, covering more than 30 million km2, with a wide biodiversity of wildlife (Griffiths 2005).
The degree of socioeconomic development and the historical and cultural circumstances of African countries (for example, the influence of European colonization) have influenced local food habits. Great diversity is found, from extreme poverty in sub‐Saharan Africa to the high degree of development of South Africa, passing through different grades of development in other areas. The countries in the north, bordering the Mediterranean, have a greater influence from Europe while those to the east may be more influenced by Asia (Chabal 2001).
Geographical location and distance to fresh produce markets, season of the year, age and gender, ethnicity or religion may all influence food habits. For example, religious celebrations or rituals may be accompanied by eating specific meals with indigenous ingredients and autochthonous vegetables. Considering all these circumstances, Jansen van Rensberg et al. (2007) showed that in South Africa, poor households use wild leafy vegetables more than wealthier ones. In another study undertaken in Uganda by Tabuti et al. (2004), the consumption of wild plants was limited to casual encounters, periods of food shortages, and as supplements to major food crops.
In this context, a wide variety of plants is used in daily life for food, water (for example, watermelons have been used as a source of water in dessert), shelter, firewood, medicine, and other necessities (van Wyk & Gericke 2000), from the ancestral traditions of indigenous people to the present day. The River Nile region and eastern Africa are among the earliest places where humans experimented with primitive food production strategies including hunting, gathering, and primal cultivation (Brandt 1984; Hadidi 1985).
Thus, the African population has a long history of using indigenous leafy vegetables, which contribute significantly to household food security and add variety to cereal‐based staple diets. These vegetables are often generically called “spinach,” are gathered predominantly by women, and may be eaten raw, cooked, or together with starchy foods (for example, in a porridge). A single plant species may be eaten or a combination of different species, alone or mixed with other ingredients, such as oil, butter, groundnuts, coconut, milk, tomato or onion (Uusiku et al. 2010). For many, the traditional names are indicative of the fact that they are usually eaten; for example, Lanatana trifolia L., traditionally eaten in Ethiopia, is called “yerejna kollo” in the Amharic language, which means “shepherd’s snack” (Asfaw & Tadesse 2001).
Despite these ancient practices, many African autochthonous vegetables have become underutilized in favor of introduced nonnative vegetables (such as spinach or cabbage, among others); however, some studies show that indigenous species, when available, are still preferred to other exotic vegetables (Marshall 2001). The decline in the use of indigenous vegetables by many rural communities has resulted in poor diets and increased incidence of nutritional deficiency disorders in many parts of Africa (Odhav et al. 2007).
The main nutritional problem in many of these areas is chronic undernutrition, affecting some 200 million people. Sub‐Saharan Africa has the highest prevalence of undernutrition in the world: one‐third of the population is chronically hungry, the majority of whom live in rural areas, and high numbers of children are suffering the consequences of this problem. Food problems affect each country differently, the dryer Sahelian countries being more prone to food shortages and starvation than forested ones (Lopriore & Muehlhoff 2003). Malnutrition in Africa manifests as protein‐energy malnutrition, but also as vitamin and mineral deficiencies.
Africa has the highest prevalence of anemia and vitamin A deficiency in the world; these are two of the three major micronutrient deficiencies recognized by the WHO (iron, iodine, and vitamin A), and considered as a moderate‐to‐severe public health problem in most African countries, especially those in the central part of the continent, where almost half the population are affected by one of these deficiencies. According to WHO data (Benoist et al. 2008), 67.6% of preschool‐aged children (<5 years old), 57.1% of pregnant women, and 47.5% of nonpregnant women of fertile age are affected by anemia (meaning more than 83, 17, and 69 million individuals affected, respectively). The prevalence of vitamin A deficiency in Africa is around 42%, with more than 56 million preschool‐aged children and more than 4 million pregnant women suffering biochemical vitamin A deficiency (low levels of serum retinol), as well as 2.5 million preschool‐aged children and 3 million pregnant women suffering from night blindness (WHO 2009). It is estimated that over 228 000 deaths of children under five which occur each year in the Economic Community of West African States (ECOWAS) countries (Benin, Burkina Faso, Cape Verde, Côte d’Ivoire, The Gambia, Ghana, Guinea, Guinea‐Bissau, Liberia, Mali, Mauritania, Niger, Nigeria, Senegal, Sierra Leone, and Togo) are attributable to vitamin A deficiency (Aguayo 2005; Sifri et al. 2003).
Regarding other nutrients, with the exception of relatively small local surveys, there are insufficient data to make a reliable estimation of the prevalence of their deficiency in the world, as their adverse effects on health are sometimes nonspecific and the public health implications are less well understood. However, national survey data from a few countries suggest that deficiencies of zinc, calcium, folate or vitamin D make a substantial contribution to the global burden of disease (Allen et al. 2006).
Also fiber intake is limited, which is aggravated by the migration of communities from rural areas to cities, often introducing a diet with high sugar and fat and low fiber content. A study undertaken by Ruel et al. (2005) on 10 sub‐Saharan countries showed that none of them reached the WHO/FAO recommended minimum daily intake of fruits and vegetables. A diversified diet would be needed to meet the daily micronutrient requirements, and particularly, diets low in fiber and micronutrients could be improved with a higher intake of fruits and vegetables; these foods have also been shown to provide many bioactive compounds of great interest in the prevention of diet‐related diseases. In this context, traditional vegetables grow wild and readily available in the field; as they are autochthonous species adapted to soil and climate, they do not need formal cultivation techniques, such as water supplies (an important problem in many areas) or other agricultural strategies often needed for horticultural crops.
Although the food use of wild greens by indigenous African populations is well known, their socioeconomic situation has delayed the gathering of scientific knowledge about this topic. The analysis of the chemical composition of African wild edible or medicinal species, in terms of nutrients, bioactive compounds or pharmacological activities, is recent. Many analyses focus on the medicinal properties of these wild plants or their essential oils, testing traditionally known properties or searching for medicinal applications.
The first studies about nutritional value of indigenous African wild vegetables were published in the late 1970s, for example that of Saleh et al. (1977) in Egypt. In the last 20 years some work has been conducted, mainly in South Africa (Afolayan & Jimoh, 2009; Kruger et al. 1998; Nesamvuni et al. 2001; Odhav et al. 2007; Steyn et al. 2001). Studies undertaken in the Mediterranean countries of North Africa often focus mainly on the study of wild plant essential oils, aromatic plants and spices, as well as wild fruits composition (for example, Boudraa et al. (2010) in Argelia, Akrout et al. (2012) in Tunisia, Imelouane et al. (2011) and Rsaissi et al. (2013) in Morocco) rather than wild greens (Tlili et al. (2009), conducted in Tunisia). Only a few works have been published on the nutritional composition of wild leafy vegetables, from Nigeria (Isong & Idiong 1997; Lockett et al. 2000), Ghana (Wallace et al. 1998), Malawi (Mosha & Gaga 1999), Senegal (Ndong et al. 2008), Cameroon (Bouba et al. 2012) and Kenya (Orech et al. 2007).
Wild greens usually have an energy value and proximal composition close to cultivated vegetables, with 3–10 % of available carbohydrate content. Odhav et al. (2007) reported values near 10% for Physalis viscosa L., Senna occidentalis (L.) Link or Solanum nodiflorum Jacq. aerial parts, gathered in South Africa. Some exceptions of leafy vegetables especially rich in carbohydrates can be found, such as the leaves of Manihot esculenta Crantz., with 18 g/100 g, or Adansonia digitata L. (baobab), with 16 g/100 g (FAO 1990; Kruger et al. 1998). Baobab leaves are rich in mucilage and widely used in soups as a vegetable in tropical Africa, or sun‐dried, ground and powdered (“lalo”) for seasoning in West Africa (FAO 1988). Lipid content is usually below 1%, with some exceptions such as Centella asiatica L. Urb., Ceratotheca triloba (Bernh.) E. May. ex Bernh., and Senna occidentalis (around 2% according to Odhav et al. (2007)). In some cases, wild leafy vegetables may have a considerable protein content, up to 2–7%, higher than the protein content of many commercial vegetables with the exception of certain legumes, as reported by Odhav et al. (2007) and Kruger et al. (1998). The leaves and shoots of some Moringa species (horse radish, eaten raw in salads like cress or cooked as a vegetable) are a good example, showing around 6–7 g of protein per 100 g of fresh plant, with high levels of the essential amino acid methionine (FAO 1988; Yang et al. 2006). Although plant proteins are not high quality in terms of covering essential amino acid needs, they could still provide a contribution to the highly deficient protein intake in many African populations. Carbohydrates, lipids, and proteins are the main contributors to energy value, ranging around 50–300 kcal/100 g fresh weight (fw) (Odhav et al. 2007; Uusiku et al. 2010), which is not a high value taking into account the high energy requirements of undernourished populations.
However, the main contribution of wild greens to the African diet is in terms of micronutrients and bioactive compounds. Table 7.1 presents data on the relevant levels of vitamins and minerals in wild leafy vegetables traditionally consumed in Africa obtained from scientific literature. Only data on species with significant nutrient content have been recorded: 100 g of fresh material providing more than 15% of generally accepted daily recommendations such as the FNB (Food and Nutritition Board) of the American Institute of Medicine (Trumbo et al. 2002) or FAO/WHO (2004). However, many other species have been traditionally eaten and reported as good contributors to the human diet; a wide variety of them are compiled in FAO (1988).
Table 7.1 Leafy vegetables traditionally consumed in Africa, standing out as sources of vitamins or minerals. Data are given per 100 g of fresh weight.
| Species | Vitamins | Minerals | References |
| Adansonia digitata L. | Vitamin C (52 mg/100 g) | Ca (208–518 mg/100 g); Fe (9.59 mg/100 g); Mn (0.56 mg/100 g) | FAO 1990; Lockett et al. 2000 |
| Amaranthus spp. (A. viridis L., A. caudatus L., A. gracilis Desf., A. hybridus L., A. dubius Mart., A. spinosus L.) | RE* (327 µg/100 g); vitamin B9 (64 µg/100 g); vitamin C (22–126 mg/100 g) | Ca (253–425 mg/100 g); Mg (105–268 mg/100 g); Fe (0.5–9.8 mg/100 g); Zn (1.35–8.4 mg/100 g); Mn (0.27–12.3 mg/100 g) | FAO 1990; Kruger et al. 1998, Nesamvuni et al. 2001; Steyn et al. 2001; Odhav et al. 2007 |
| Asystasia gangetica L. | – | Ca (385 mg/100 g); Mg (144 mg/100 g); P (122 mg/100 g); Fe (2.55 mg/100 g); Mn (2.7 mg/100 g) | Odhav et al. 2007 |
| Bidens pilosa L. | RE* (301–985 µg/100 g); vitamin B9 (351 µg/100 g); vitamin C (23 mg/100 g) | Ca (162–340 mg/100 g); Mg (79–157 mg/100 g); Fe (2–6 mg/100 g); Cu (1.2 mg/100 g) | FAO 1990; Kruger et al. 1998; Odhav et al. 2007 |
| Brassica spp. | Vitamin C (30–113 mg/100 g) | – | Kruger et al. 1998; Mosha & Gaga 1999 |
| Ceratotheca triloba (Bernh.) E.May. ex Bernh. | – | Fe (2.9 mg/100 g); Mn (1.2 mg/100 g) | Odhav et al. 2007 |
| Centella asiatica Urb. | – | Ca (291 mg/100 g); Mg (32.5 mg/100 g); Fe (2.16 mg/100 g); Mn (2.76 mg/100 g) | Odhav et al. 2007 |
| Chenopodium album L. | RE* (917 µg/100 g); vitamin C (31 mg/100 g) | Ca (250–330 mg/100 g); Mg (109–211 mg/100 g); Fe (2.1–6.1 mg/100 g); Zn (1.4–18.5 mg/100 g); Mn (1.8–4.6 mg/100 g) | Kruger et al. 1998; Odhav et al. 2007; Afolayan & Jimoh 2009 |
| Cleome spp. (C. gynandra L., C. monophylla L.) | RE* (663–1536 µg/100 g); vitamin B9 (346–418 µg/100 g); vitamin C (13–50 mg/100 g) | Ca (206–384 mg/100 g); Mg (44–76 mg/100 g); Fe (2.6–9.7 mg/100 g); Mn (1.2 mg/100 g) | FAO 1990; Kruger et al. 1998; Nesamvuni et al. 2001; Odhav et al. 2007 |
| Corchorus olitorius L. | vitamin C (38 mg/100 g); RE (966 µg/100 g) | Fe (2 mg/100 g) | Saleh et al. 1977; Orech et al. 2007 |
| Corchorus tridens L. | RE* (533 µg/100 g) | Ca (363 mg/100 g); Mg (73 mg/100 g); Fe (11.5 mg/100 g) | Nesamvuni et al. 2001 |
| Cucumis metuliferus Naudin | – | Ca (386 mg/100 g); Mg (132 mg/100 g); Fe (2.4 mg/100 g); Mn (0.52 mg/100 g) | Odhav et al. 2007 |
| Cucurbita pepo L. | RE* (194 µg/100 g); vitamin C (11 mg/100 g) | – | Kruger et al. 1998 |
| Emex australis Steinh. | – | Mg (1.7 mg/100 g); Zn (2.2 mg/100 g); Mn (3.41 mg/100 g) | Kruger et al. 1998; Odhav et al. 2007 |
| Euphorbia hirta L. | – | Ca (176 mg/100 g); Zn (5.29 mg/100 g) | Wallace et al. 1998 |
| Ficus thonningii Blume | – | Ca (285 mg/100 g); Mg (45.3 mg/100 g); Fe (5.12 mg/100 g); Mn (1.33 mg/100 g) | Lockett et al. 2000 |
| Galinsoga parviflora Cav. | – | Fe (3 mg/100 g) | – |
| Grewia occidentalis L. | – | Ca (183 mg/100 g); Mg (130 mg/100 g); P (76 mg/100 g) | Steyn et al. 2001 |
| Hibiscus trionum L. | – | Ca (2171 mg/100 g); Mg (731 mg/100 g); P (290 mg/100 g); Zn (5.7 mg/100 g) | Steyn et al. 2001 |
| Hibiscus manihot L. | – | Ca (322 mg/100 g); Mg (244 mg/100 g); Fe (141 mg/100 g) | Aalbersberg et al. 1991 |
| Ipomoea batatas (L.) Lam. | RE* (103–980 µg/100 g); vitamin B9 (80 µg/100 g); vitamin C (11–70 mg/100 g) | Mg (61 mg/100 g) | FAO 1990; Kruger et al. 1998; Mosha & Gaga 1999 |
| Justicia flava Vahl. | – | Ca (331 mg/100 g); Mg (225 mg/100 g); Fe (2.6 mg/100 g); Zn (1.8 mg/100 g); Mn (1.3 mg/100 g) | Odhav et al. 2007 |
| Manihot esculenta Crantz | RE* (1970 µg/100 g); vitamin B9 (80 µg/100 g); vitamin C (311 mg/100 g) | – | FAO 1990; Kruger et al. 1998 |
| Momordica balsamina L. | – | Ca (403 mg/100 g); Fe (3.4–3.5 mg/100 g); Zn (1.8 mg/100 g); Mn (1.5 mg/100 g) | Odhav et al. 2007 |
| Moringa oleifera Lam. | – | Ca (111–141 mg/100 g); Fe (4.3–5.7 mg/100 g); Mn (0.46 mg/100 g) | Lockett et al. 2000; Ndong et al. 2008 |
| Moringa peregrina Fiori | RE* (400 µg/100 g); vitamin C (264 mg/100 g) | Ca (458 mg/100 g); Fe (5.6 mg/100 g) | Yang et al. 2006 |
| Moringa foetida Schumach | RE* (901 µg/100 g); vitamin C (20 mg/100 g) | – | Nesamvuni et al. 2001 |
| Opuntia microdasys (Lehm.) Pfeiff | – | Ca (2.4 mg/100 g); Mg (5.8 mg/100 g); K (10 mg/100 g) | Chahdoura et al. 2015 |
| Opuntia macrorhiza (Engelm.) | – | Ca (3 mg/100 g); Mg (1.6 mg/100 g); K (4.3 mg/100 g) | Chahdoura et al. 2015 |
| Oxygonum sinuatum Dammer | – | Mg (41.6 mg/100 g); Fe (3.12 mg/100 g) | Odhav et al. 2007 |
| Physalis viscosa | – | Mg (101 mg/100 g); Fe (3.8 mg/100 g) | Odhav et al. 2007 |
| Portulaca oleracea L. | – | Fe (2.9 mg/100 g); Zn (2.4 mg/100 g); Mn (1.68 mg/100 g) | Odhav et al. 2007 |
| Rumex spp. | Vitamin C (121 mg/100 g) | – | Saleh et al. 1977 |
| Scandicium stellatum Thell. | Vitamin C (196 mg/100 g) | – | Saleh et al. 1977 |
| Senna occidentalis (L.) Link. | – | Ca (513 mg/100 g); Mg (1.61 mg/100 g); Fe (2.5 mg/100 g); Zn (2.1 mg/100 g) | Odhav et al. 2007; Kruger et al. 1998 |
| Sonchus asper (L.) Hill. | – | Ca (344 mg/100 g); Mg (69.8 mg/100 g); Fe (22.4 mg/100 g); Mn (1.17 mg/100 g) | Afolayan & Jimoh 2009 |
| Sonchus oleraceus L. | Vitamin C (67 mg/100 g) | Ca (193 mg/100 g); Mg (50.7 mg/100 g); Fe (14.9 mg/100 g) | Saleh et al. 1977; Steyn et al. 2001 |
| Spinacia oleracea L. | RE* (669 µg/100 g); vitamin B9 (194 µg/100 g); vitamin C (28 mg/100 g) | Mg (79 mg/100 g); Fe (2.7 mg/100 g) | Kruger et al. 1998; Steyn et al. 2001 |
| Trigonella foenum‐graecum L. | Vitamin C (207 mg/100 g) | – | Saleh et al. 1977 |
| Urtica urens L. | – | Mg (292 mg/100 g); Mn (4.45 mg/100 g) | Kruger et al. 1998; Odhav et al. 2007 |
| Vernonia spp. | Vitamin C (51–198 mg/100 g) | Ca (123 mg/100 g); Fe (3.5 mg/100 g); Mn (0.69 mg/100 g) | FAO 1990; Lockett et al. 2000; Ejo et al. 2007 |
| Vigna unguiculata (L.) Walp. | RE* (99 µg/100 g); vitamin B9 (141 µg/100 g); vitamin C (50 mg/100 g) | Ca (188 mg/100 g); Mg (60 mg/100 g) | Kruger et al. 1998 |
| Wahlenbergia undulata A. DC. | – | Ca (38.6 mg/100 g); Fe (3.8 mg/100 g); Mn (1.4 mg/100 g) | Kruger et al. 199;, Odhavet al. 2007 |
* RE (= retinol equivalents) are usually calculated as (content of β‐carotene/6) + (contents of other provitamin A carotenoids /12), according to Mahan et al. (2012).
From a nutritional point of view, minerals can be divided into macroelements and microelements. Among macroelements, calcium is one of the most important, since a deficiency in calcium intake in infants may induce rickets, while in the elderly it leads to the development of osteoporosis and tetany in skeletal muscles (Mahan et al. 2012; Schrager 2005). High calcium intake should be achieved during the development of bone mass, in the earlier stages of life. A dietary calcium range of 210–800 mg/day is recommended for infants and younger children, while adults need 700–1000 mg/day (Cuervo et al. 2009). These levels take into account factors affecting calcium bioavailability, such as individual conditions, as well as the form present in the food, and the presence of components enhancing or decreasing its absorption.
Although leafy vegetables contain abundant calcium, with levels even higher than many foods widely accepted as good calcium sources, such as dairy products, they are also one of the main sources of oxalates in the diet, which are assumed to have a negative impact on mineral absorption due to their ability to bind free minerals in the small intestine, forming insoluble oxalates that remain nonabsorbed in the gut. Generally, oxalic acid may reduce calcium absorption by about one‐sixth, so foods with a ratio of oxalic acid/Ca lower than 2.5 are preferably for humans (Concon 1988; Derache 1990; Mahan et al. 2012).
To the authors’ knowledge, there is little published information about oxalate content in African wild leafy vegetables; however, some species growing in Africa are known to contain high oxalate levels (for example, Portulaca oleracea L., Chenopocium album L., some Rumex spp. or Amaranthus spp. leaves) (Bianco et al. 1998; FAO 1988; Morales et al. 2014; Sánchez‐Mata & Tardío 2016). Ilelaboye et al. (2013) reported levels below 50 mg/100 g of oxalates, 84–313 mg/100 g of phytates, and less than 10 mg/100 g of tannins in leaves of African Amaranthus hybridus L., Colocasia esculenta Schott., Solanum nigrum L., Telfairia occidentalis Hook. f., or Crassocephalum crepidioides S. Moore, with good oxalic acid/Ca ratio. When cooking these species, minerals were heat stable, but they lixiviated to the cooking liquid, as well as antinutrients such as oxalates, phytates or tannins, as shown by Ilelaboye et al. (2013).
Even taking into account the presence of these antinutrients with their ability of complexing mineral elements, many wild African species stand out for their very high calcium levels, which, although not totally bioavailable, may be considered as an interesting contribution in a diet that is poor in dairy products for different reasons (low access to milk and high prevalence of lactose intolerance in the African population) (Lomer et al. 2008; Pettifor 2004).
Vegetables such as Adansonia digitata L., Amaranthus spp., Momordica spp. or Senna occidentalis (L.) Link stand out (see Table 7.1), with calcium levels higher than 400 mg/100 g of fresh product, meaning that, with a 100 g portion of these greens, nearly half of the daily recommended levels of calcium for adults could be achieved, and this ratio would be even higher for infants. There are not many data about oxalate levels in the leaves of these species but in some cases, they have exhibited low levels (as previously mentioned for Amaranthus hybridus). According to the FAO (1988), calcium present in fresh young baobab leaves (A. digitata) may be better absorbed than that from other greens. Hibiscus trionum L. is also remarkable, reaching 2 g of calcium/100 g (see Table 7.1).
Regarding other macroelements, Table 7.1 shows that magnesium is abundant in Amaranthus spp., Asystasia gangetica T. Anderson, Bidens pilosa L., Chenopodium album, Grewia occidentalis L. and Justicia flava Vahl edible parts.
Iron is also a very important element for the diet of African populations, since high iron losses or low iron intakes cause anemia, with infants below two years old, adolescent girls, and pregnant women being the main groups at risk. Most institutions recommend 8–10 mg Fe/day for men and elderly women, and about 16–20 mg/day for women below 50–55 years old due to menstruation (Cuervo et al. 2009).
Iron is present in foods either as heme Fe in animal tissues or nonheme Fe (inorganic) in plant tissues, such as legumes and vegetables. The former is more easily absorbed (bioavailability of 20–30%), while only 2–10% of inorganic Fe is absorbed (Bothwell et al. 1989). Despite the poor absorption of plant origin iron, it represents a contribution that should be taken into account in populations with difficult access to animal origin foods such as meat. Iron sources with easy accessibility such as autochthonous plants are thus of great importance in improving the quality of the African diet.
In this respect, Adansonia digitata and Amaranthus spp. edible parts may reach almost 10 mg Fe/100 g fw, which is a similar level to those found in legume seeds or vegetables traditionally considered as good iron sources such as spinach (around 2–4 mg/100 g, according to Souci et al. (2008)). Also, some Sonchus species have been shown to present 14–23 mg Fe/100 g, a very high level for a plant food. Van der Walt et al. (2009) indicate a very high value of iron in samples of Amaranthus thunbergii Moq. leaves (up to 237 mg/100 g dry weight) and Sena et al. (1998) reported values around 120 mg/100 g dry weight in Hibiscus spp. and Ceratotheca sesamoides leaves. This means that, despite the inorganic nature of this nutrient, this amount represents a considerable contribution to the daily dietary iron recommendations.
As previously indicated, different species should be regarded as interesting alternatives to improve the mineral intake in these populations (Freiberger et al. 1998; Sena et al. 1998). For example, Amaranthus spp. have shown high levels of Ca, Mg, Fe, Zn, and Mn, according to different studies (FAO 1990; Kruger et al. 1998; Nesamvuni et al. 2001; Odhav et al. 2007). Also Hibiscus trionum, analyzed in a study conducted in South Africa by Steyn et al. (2001), is remarkable for its high levels of Ca, Mg, P, and Zn. The encouragement of the inclusion of these indigenous species in the diet of African populations could possibly ameliorate some of their nutritional problems.
Vitamins are one of the most relevant contributions of vegetables to the diet. Due to the high water content and low lipid amount, hydrosoluble vitamins are more important in vegetables than liposoluble ones. Leafy vegetables are well known as good folate sources, and an increase in their consumption would be a good strategy to avoid the consequences of folate deficiencies, mainly defects in neural tube formation (spina bifida or anencephaly), among other disorders (Kondo et al. 2005). To avoid these diseases, a daily intake of 200–400 µg/day, mainly in the preconception period, is recommended; in all cases an additional 100–200 µg/day should be ingested during pregnancy (especially in the first months, to reduce the risk of neural tube formation defects) and lactation, according to different national and international recommendations recorded by Cuervo et al. (2009). In this respect, African wild leafy vegetables such as Bidens pilosa or Cleome spp. provide more than 300 µg folate/100 g of fresh plant (see Table 7.1). Both are abundant weeds, very widely used across Africa; B. pilosa (blackjack) leaves are very popular as a pot‐herb (although certain authors regard it as an irritant), and Cleome gynandra L. is eaten regularly in Malawi, while in Kenya it is reserved for special occasions and ceremonies, as well as for women in labor. The folate content of both species is in the range of or even higher than many cultivated vegetables (Souci et al. 2008), making them interesting options whose consumption should be encouraged, especially for African women.
As for C. gynandra or C. monophylla L., these plants have shown good nutritional potential as sources of folate but also for their vitamin C content. Vitamin C deficiency provokes scurvy, whose primary symptoms are haemorrhage in the gums, skin, bones, and joints, and the failure of wound healing. Fresh fruits and vegetables are the best sources of vitamin C, and wild edible species are no exception. Many wild leafy vegetables of Amaranthus and Brassica spp. are remarkable for containing more than 100 mg of ascorbic acid/100 g fresh plant, reaching almost 200 mg/100 g in Vernonia spp.
Dietary recommendations for vitamin C are established with a wide range of variation (45–120 mg/day for adults); however, many of these species can provide the whole daily requirement in one 100 g portion. A limitation of this contribution is the fact that vitamin C is a very heat‐labile compound so very variable losses of this vitamin may occur, depending on the way of cooking vegetables, from 14% to 95% (Morales 2012; Somsub et al. 2008; Yadav et al. 1997). In this way, raw consumption of the plants is recommended if possible, and if the plant has to be processed, pressure or steam cooking, when available, is usually preferable to traditional methods to minimize these losses.
Regarding liposoluble vitamins, reference should be made to vitamin A, which is present in food plants not as retinol but as provitamin A carotenoids (α‐carotene, β‐carotene, and β‐cryptoxanthin), which are biotransformed to retinol in the human body (Britton et al. 1995; Ibrahim et al. 1991; Patton et al. 1990). Their vitamin A activity is measured as retinol equivalents (RE). Besides this, most carotenoid compounds play an important role as dietary antioxidants. Additionally, lutein and zeaxanthin may be protective for eye disease because they absorb damaging blue light that enters the eye (Krinsky & Johnson 2005). Other nonprovitamin A carotenoids important in plant tissues include neoxanthin and violaxanthin (frequent in leafy vegetables) and lycopene (present in some fruits).
Food sources of these compounds include a variety of fruits and vegetables. Some authors have measured provitamin A activity in some African wild edible plants from their carotenoid contents. Not many studies include a pormenorized analysis of carotenoids in African wild vegetables; however, Tlili et al. (2009) reported lutein and β‐carotene as major carotenoids in Tunisian leafy vegetables, particularly in Capparis spinosa L. edible parts, at levels of 1234 mg/100 g and 234 mg/100 g respectively, while other carotenoids were present in much lower amounts.
As previously mentioned, deficiency of vitamin A is a major cause of premature death in developing countries, particularly among children, and manifests with xerophthalmia, night blindness, poor reproductive health, increased risk of anemia, and slowed growth and development (FAO/WHO 2004). The daily intake of vitamin A for adults should range between 0.5 and 1 mg RE/day to avoid these problems (Cuervo et al. 2009). Among African wild edible plants, again B. pilosa stands out as a good source of vitamin A, reaching almost 1 mg RE, which means that a 100 g portion can provide the total daily requirement for an adult; other leafy vegetables are also good alternatives to improve vitamin A status, as can be seen in Table 7.1. This is the case for Ipomoea batatas L. (sweet potato) and Manihot esculenta Crantz (cassava), both of them more widely known for the use of their tubers but whose leaves are also eaten in many tropical areas of Africa and Asia. The leaves of sweet potato may reach up to 1 mg RE/100 g. Cassava leaves have been reported to provide almost 2 mg RE/100 g, while the leaves of different Cleome and Corchorus aspecies (both of them very popular in different part of Africa) have shown high RE levels. Also, Momordica foetida Schumach (bitter melon) leaves contain almost 1 mg RE/100 g; the fruits of Momordica species are also eaten (some varieties are bitter, due to the presence of momordicoside, a special type ofcucurbitacin), usually removed by soaking in salt water, boiling or frying (Gry et al. 2006).
These findings are of great importance in areas where half the population is suffering from vitamin A deficiency, since these autochthonous plants could be easily gathered or adapted to cultivation with great nutritional benefit, especially for children and other at‐risk groups. Many authors have reported on the cultivation of wild African edible species, such as Amaranthus spp. or Corchorus spp. (Aju et al. 2013; FAO 1988; Mathowa et al. 2014).
Other bioactive compounds in African wild vegetables include dietary fiber and phenolic compounds. Fiber has been measured in several wild plant foods and many of them have shown more than 3 g/100 g fw, the level commonly used as a minimum to indicate that a food is rich in fiber (European Parliament and Council 2006); some plants even contain more than 6 g/100 g fw, as in the case of Urtica urens L. and Euphorbia hirta L. edible parts (6.7 and 7.7 g/100 g fw, respectively); this information can be seen in Table 7.2. These species could contribute to the dietary fiber intake in African populations, improving their gastrointestinal health, as well as other effects of dietary fiber, such as those related to regulatory activity of the immune system (Brett & Waldron 1996).
Table 7.2 Leafy vegetables traditionally consumed in Africa, standing out as sources of bioactive compounds. Data are given per 100 g of fresh weight.
| Species | Dietary fiber (g/100 g) |
Carotenoids/phenolic compounds/tocopherols | References |
| Adansonia digitata L. | 3 | – | FAO 1990 |
| Amaranthus spp. | 3–3.3 | Carotenoids (88–194 mg/100 g dw); total phenols (1057–2181 mg GAE/100 g dw) | Nesamvuni et al. 2001; Odhav et al. 2007 |
| Bidens pilosa L. | 3–6 | – | FAO 1990, Kruger et al. 1998; Nesamvuni et al. 2001, Odhav et al. 2007 |
| Capparis spinosa L. | – | Lutein (234 mg/100 g); β‐carotene (104 mg/100 g); neoxanthin (4.55 mg/100 g); violaxanthin (1.77 mg/100 g); α‐tocopherol (20.2 mg/100 g) | Tlili et al. 2009 |
| Chenopodium album L. | – | Total phenols (8.61 mg TAE/g extract); proanthocyanidins (3.8 mg CE/g extract) | Afolayan & Jimoh 2009 |
| Cleome spp. (C. gynandra L., C. monophylla L.) | 2.7–4.5 | – | Nesamvuni et al. 2001 |
| Euphorbia hirta L. | 7.7 | Tannins (1222 mg/100 g) | Wallace et al. 1998 |
| Ipomoea involucrata Hance | – | Tannins (869 mg /100 g) | Wallace et al. 1998 |
| Lesianthera africana L. | 4 | – | Isong & Idiong 1997 |
| Manihot esculenta L. | 4 | – | Odhav et al. 2007 |
| Momordica foetida L. | 3–3.15 | – | FAO 1990, Nesamvuni et al. 2001 |
| Moringa peregrina Fiori | Tocopherols (28 mg/100 g) | Yang et al. 2006 | |
| Opuntia microdasys (Lehm.) Pfeiff. | 5.4 | Tocopherols (6.9 mg/100 g dw); hexosyl ferulic acid (852 µg/g extract); isorhamnetin O‐(rhamnosyl)‐rutinoside (2507 µg/g extract) | Chahdoura et al. 2014 |
| Opuntia macrorhiza (Engelm.) | 6.2 | Tocopherols (5.1 mg/100 g dw); piscidic acid (3400 µg/g extract); eucomic acid (1688 µg/g extract) | Chahdoura et al. 2014 |
| Senna occidentalis L. | 3 | – | Odhav et al. 2007 |
| Sonchus asper L. | – | Total phenols (10.5 mg TAE/g extract); proanthocyanidins (2.2 mg CE/g extract) | Afolayan & Jimoh 2009 |
| Spinacia oleracea L. | 3 | – | Kruger et al. 1998 |
| Urtica urens L. | 6.9 | Total phenols (6.7 mg TAE/g extract); Proanthocayanidins (3.9 mg CE/g extract) | Afolayan & Jimoh 2009 |
| Vigna unguiculata L. | 4 | – | Kruger et al. 1998 |
| Xanthosomas spp. | – | Tannins (655 mg/100 g) | Wallace et al. 1998 |
CE, catechin equivalent; dw, dry weight; GAE, gallic acid equivalent; TAE, tannic acid equivalent.
Euphorbia hirta also stands out as a good source of phenolic compounds, with more than 1 g of tannins per 100 g of fresh plant (Wallace et al. 1998); this is probably related to high antioxidant activity in this species. In vegetables, often tannins are bound to fiber polymers and remain undigested in the gut, acting as antioxidants at this level. In this case, the presence of a high amount of fiber and tannins together suggests a very interesting effect of this plant at gastrointestinal level, so it would be a very good choice for food. Many of the reports about phenolic content in wild African plants are focused on medicinal plants (Boulanouar et al. 2013; Djeridane et al. 2007) rather than food plants, searching for biological/pharmacological activities of these compounds as antimicrobial, antioxidant or antiinflammatory agents. For example, the aqueous extract of Urtica urens has shown antimicrobial activity against several Gram‐positive and Gram‐negative microorganisms, comparable to some antibiotics (Jimoh et al. 2010), and U. dioica L. has shown great potential for the treatment of urinary pathologies (Zhang et al. 2014). Lindsey et al. (2002) studied wild food plants growing widely in South Africa, finding that extracts from greens such as Sisymbrium thellungii O. E. Schulz, Hypoxis hemerocallidea Fisch., C. A. Mey. & Avé‐Lall, and U. dioica showed interesting properties for the inhibition of lipid peroxidation. More studies would be desirable to determine the pormenorized composition of phenolics or other compounds responsible for these actions in African wild vegetables, which could help to improve the antioxidant potential of African diets.
In many African countries, different food‐based strategies, driven by nongovernmental organizations and other local institutions, have already met with good results and acceptance (Oniang’o et al. 2008; Smith & Eyzaguirre 2007), in the move to improve the nutritional quality of African diets.
The American continent is a good example of economic, social, and cultural differences, from the countries in the north, with a high degree of economic development, to Central and South America, where areas with a better economic status are mixed with more depressed areas. Many factors have contributed to this map, including historical, demographic, and political reasons, among others. Due to the size and geographical characteristics of the continent, almost all the different types of climates can be found, from polar to tropical, which enormously influences the vegetation and human relationship with the environment (Kottek et al. 2006).
The tribes of ancient inhabitants across the whole continent were very well adapted to the natural world. According to the first chronicles of European explorers, they interacted every day with the native plants and animals, transforming plants, animals, and soil materials into food, medicines, and utensils for daily life. Many tribes were nomads, and this made it possible to gather plants from different places, not randomly but with a clear objective of protecting wild animal and plant populations, as a part of their own lives, preserving spectacular landscapes, such as prairies, forests, grasslands, and savannahs, and achieving an intimacy with wildlife unmatched by any of the modern trends of returning to nature (Anderson 2005; Barrera et al. 1977).
Later, European colonization contributed to great changes in landscape, agricultural practices, society, and food habits, and subsequent evolution has brought about the loss of a great part of the cultural heritage of indigenous people (Anderson 2005; Stoffle et al. 1990). Nowadays, in the most developed countries, gathering of wild plants has been replaced by use of cultivated foods and intensive agriculture practices, and very few of these ancient traditions exist, linked to small areas of indigenous population remaining in reserves or similar places. In other countries, where indigenous characteristics remain in many aspects of life and traditions, the presence of wild vegetables in the diet has been better preserved, and many wild plants can be found in the gastronomy of these countries, gathered from the wild, sold in local markets or cultivated in house gardens, as a part of sustainable development of many rural communities (Herrera Molina et al. 2014a).
The American continent presents huge social differences, making it possible to find the two extremes of malnutrition: the type linked to abundance of food (overweight, obesity, diabetes, cardiovascular disease or metabolic syndrome), often accompanied by subclinical deficiencies of some vitamins and minerals caused by the lack of fresh fruit and vegetable intake, and the type suffering the consequences of undernutrition. According to WHO data (Benoist et al. 2008), 29.3% of preschool‐aged children (<5 years old), 24.1% of pregnant women, and 17.8% of nonpregnant women of fertile age are affected by anemia. The prevalence of vitamin A deficiency in America is around 15.6%, with more than 8 million preschool children suffering from biochemical vitamin A deficiency and low levels of serum retinol (WHO 2009). In rural communities eating a wide variety of fresh fruits and vegetables which provide vitamins, minerals, fiber, and other bioactive compounds, health status is usually good, and the displacement of autochthonous foods by the introduction of less healthy habits (often linked to consumption of modern diets) should be avoided for cultural and nutritional reasons.
Tables 7.3 and 7.4 present data about wild plant nutrients and bioactive compounds. Some vegetables, such as Allium vineales L., Glechoma hederacea L. or Plantago major leaves, can be highlighted for their high contribution of vitamin A (10 000–19 000 IU per 100 g, around 0.5–1 mg RE/100 g); they could be a tool to improve the vitamin status of American populations. Vitamin C is abundant in the leaves of Alliaria officinalis L. and Allium species, with values of more than 80 mg/100 g, higher than many cultivated foods generally considered as vitamin C sources (e.g. citric fruits). The culinary processing of these vegetables should be reduced to the minimum to preserve their vitamin C content. Very few data about the folate content of American wild vegetables are available in the literature: low levels have been reported, for example, in Urtica dioica, but as for other wild leafy vegetables eaten all over the world, many of them may have levels to improve the nutritional status of the population, especially for women of fertile age, avoiding fetal malformations linked to deficiencies of folic acid. More research should be done in this field with the purpose of establishing recommendations that could be easy to follow since in Central and South America there are many populations using wild plants in their habitual diet.
Table 7.3 Vegetables traditionally consumed in America, standing out as sources of vitamins or minerals. Data are given per 100 g of fresh weight.
| Species | Edible part | Vitamins | Minerals | References |
| North America | ||||
| Achillea millefolium L. | Leaves | – | K (645 mg/100 g); Ca (225 mg/100 g); Mg (53 mg/100 g); Fe (13.1 mg/100 g); Cu (0.2 mg/100 g); Zn (0.7 mg/100 g); Mn (4.0 mg/100 g) | Kuhnlein & Turner 1991 |
| Alliaria officinalis L. | Leaves | Vitamin C (190 mg/100 g) | – | Zennie et al. 1977 |
| Allium vineales L. | Leaves | Vitamin C (130 mg/100 g) | – | Zennie et al. 1977 |
| Allium tricoccum A.T. | Leaves | Vitamin C (80 mg/100 g) | – | Zennie et al. 1977 |
| Amaranthus palmeri S.Watson | Leaves | RE (385 mg/100 g); vitamin B2 (240 µg/100 g); B3 (1.2 mg/100 g); C (72.5 mg/100 g) | K (411 mg/100 g); Ca (362 mg/100 g); Fe (4.5 mg/100 g) | Kuhnlein & Turner 1991 |
| Amaranthus spp. | Leaves | RE (292 mg/100 g); vitamin B2 (160 µg/100 g); B3 (1.4 mg/100 g); C (43.3 mg/100 g) | K (611 mg/100 g); Ca (267 mg/100 g); MG (55 mg/100 g); Cu (0.2 mg/100 g); Fe (3.9 mg/100 g); Zn (0.9 mg/100 g) | Kuhnlein & Turner 1991 |
| Chenopodium album L. | Leaves | Vitamin B3 (120 µg/100 g); C (70 mg/100 g); K (347 µg/100 g) | Ca (246 mg/100 g); Fe (1.8 mg/100 g); Cu (2.3 mg/100 g); Zn (2.3 mg/100 g). | Kuhnlein 1990 |
| Chenopodium ambrosioides L. | Leaves | Vitamin B2 (280 µg/100 g); B3 (800 µg/100 g); C (11 mg/100 g) | Ca (304 mg/100 g); Fe (5.2 mg/100 g) | Kuhnlein & Turner 1991 |
| Cichorium intybus L. | Leaves | RE (400 mg/100 g); vitamin B3 (500 µg/100 g) | K (420 mg/100 g); Fe (0.9 mg/100 g) | Kuhnlein & Turner 1991 |
| Duschenea indica (=Potentilla indica (Andrews) T. Wolf) | Leaves | Vitamin C (79 mg/100 g) | – | Zennie et al. 1977 |
| Epilobium angustifolium L. | Young stems | – | Cu (0.7 µg/100 g) | Kuhnlein 1990 |
| Glechoma hederacea L. | Leaves | Vitamin C (44 mg/100 g) | – | Zennie et al. 1977 |
| Malva parviflora L. | Leaves | Vitamin C (65 mg/100 g) | Ca (324 mg/100 g) | Kuhnlein & Turner 1991 |
| Mentha spicata L. | Leaves | RE (856 mg/100 g); vitamin B3 (0.4 mg/100 g); C (68 mg/100 g) | Ca (200 mg/100 g); Fe (15.6 mg/100 g) | Kuhnlein & Turner 1991 |
| Oxalis stricta L. | Leaves | Vitamin C (59–79 mg/100 g) | – | Zennie et al. 1977 |
| Plantago major L. | Leaves | RE (252 mg/100 g); vitamin B2 (0.28 mg/100 g); B (0.8 mg/100 g), C (8–19 mg/100 g) | K (277 mg/100 g); Ca (184 mg/100 g) | Kuhnlein & Turner 1991 Zennie et al. 1977; |
| Porphyra perforata J. Ag. | Leaves | – | Ca (230 mg/100 g); Mg (623 mg/100 g); Fe (2.9 mg/100 g); Cu (1.7 mg/100 g) | Kuhnlein 1990 |
| Rumex acetosella L. | Young leaves | Vitamin B3 (430 µg/100 g); C (33.5 mg/100 g) | Fe (2.3 mg/100 g); Cu (1.2 mg/100 g); Zn (1.2 mg/100 g) | Kuhnlein 1990 |
| Urtica dioica L. | – | RE (2248 mg/100 g); vitamin B2 (160–220 µg/100 g); B3 (300–371 µg/100 g); C (75 mg/100 g) | Ca (236–452 mg/100 g); Mg (63–235 mg/100 g); Fe (1–1.26 mg/100 g); Zn (1.9–2 mg/100 g) | Kuhnlein & Turner 1991; Phillips et al. 2014 |
| Central America | ||||
| Agave shrevei Gentry sbsp. matapensis | Basal leaves | – | Ca (1061 mg/100 g); Mg (382 mg/100 g); Fe (5.6 mg/100 g); Zn (1.9 mg/100 g) | Laferriere et al. 1991 |
| Hedeoma patens M.E. Jones | Shoots | – | Ca (1253 mg/100 g); Mg (99.1 mg/100 g); Cu (0.8 mg/100 g); Zn (2.8 mg/100 g) | Laferriere et al. 1991 |
| Monarda austromontana Epling | Shoots | – | Ca (1303 mg/100 g); Mg (431.3 mg/100 g); Cu (1.2 mg/100 g); Zn (4.9 mg/100 g) | Laferriere et al. 1991 |
| Opuntia spp. | Cladodes | Vitamin B1 (140 µg/100 g); B2 (60–80 µg/100 g); B3 (46–240 µg/100 g); C (7–22 mg/100 g) | Ca (12.8–81 mg/100 g); Mg (16.1–98.4 mg/100 g); Fe (0.4–2.34 mg/100 g) | Feugang et al. 2015; Rosquero Perez 2001 |
| Opuntia durangensis Brilton & Rose | Cladodes | – | Ca (2422 mg/100 g); Mg (1938 mg/100 g); Fe (9.6 mg/100 g); Cu (0.2 mg/100 g) | Laferriere et al. 1991 |
| Opuntia macrorhiza Engelm. | Cladodes | – | Ca (1541 mg/100 g); Mg (917 mg/100 g); Fe (8.5 mg/100 g); Cu (1.3 µg/100 g); Zn (5.6 mg/100 g) | Laferriere et al. 1991 |
| Opuntia robusta Pfeiff. | Cladodes | – | Ca (1235 mg/100 g); Mg (839 mg/100 g); Fe (15.6 mg/100 g); Cu (0.5 mg/100 g); Zn (16.1 mg/100 g) | Laferriere et al. 1991 |
| Teloxys ambrosioides (L.) W.A. Weber | Shoots | – | Ca (1892 mg/100 g); Mg (1418 mg/100 g); Fe (12.7 mg/100 g); Cu (0.9 mg/100 g) | Laferriere et al. 1991 |
| South America | ||||
| Trichanthera gigantea Humb. & Bonpl. ex Steud. | Leaves | – | Ca (972–1242 mg/100 g); Mg (153–202 mg/100 g); Fe (2.15–8.42 mg/100 g); Cu (0.21–0.44 mg/100 g); | Leterme et al. 2006 |
| Xanthosoma spp. | Leaves | – | Ca (280–372 mg/100 g); Mg (53–104 mg/100 g); Fe (0.66–6.42 mg/100 g); Cu (0.08–0.28 mg/100 g) | Leterme et al. 2006 |
IU of vitamin A are obtained by multiplying the amount of β‐carotene (µg) by a factor of 1.6.
Table 7.4 Vegetables traditionally consumed in America standing out as sources of bioactive compounds. Data are given per 100 g of fresh weight.
| Species | Edible part | Dietary fiber (g/100 g) | Carotenoids/fatty acids (relative percentage)/phenolics | References |
| North America | ||||
| Chamerion angustifolium (L.) Holub | Aerial part | – | C18:2 (10.2–17.4%); C18:3 (35.9–40.3%) | Malainey et al. 1999 |
| Chenopodium album L. | Young leaves | 1.5 | β‐ carotene (640 µg/100 g) C18:2 (12.8–13.9%); C18:3 (34.1–35.7%) |
Kuhnlein 1990; Malainey et al. 1999 |
| Urtica spp. | Aerial part | – | C18:2 (18.7%); C18:3 (30.8%) | Malainey et al. 1999 |
| Conyza canadiensis | Aerial part | – | C18:2 (21.3%) | Malainey et al. 1999 |
| Heracleum mantegazzianum Sommier & Levier | Aerial part | – | C18:2 (20.8–27.6%); C18:3 (16.1–22.9%) | Malainey et al. 1999 |
| Lycopus americanus Muhl. | Aerial part | – | C18:2 (10.35%); C18:3 (30.71%) | Malainey et al. 1999 |
| Maianthemun racemosum L. | Aerial part | – | C18:2 (21.3–29.2%); C18:3 (27.3–37.6%) | Malainey et al. 1999 |
| Rumex spp. | Aerial part | – | C18:2 (11.6–16.4%); C18:3 (31.3–43.9%) | Malainey et al. 1999 |
| Rumex acetosella L. | Young leaves | 1.1 | – | Kuhnlein 1990 |
| Rumex crispus L. | Leaves | – | – | Chirinos et al. 2013 |
| Rubus parviflorus Nutt. | Young stems | 1.0 | – | Kuhnlein 1990 |
| Smilax ornata Lem. | Aerial part | – | C18:2 (6.38–16.3%); C18:3 (33.1–49.9%) | Malainey et al. 1999 |
| Solidago canadensis L. | Aerial part | – | C18:2 (10.5–18.1%); C18:3 (30.1–42.5%) | Malainey et al. 1999 |
| Stellaria porsildii C.C. Chinnappa | Aerial part | – | C18:2 (31.9%); C18:3 (15.1%) | Malainey et al. 1999 |
| Urtica dioica L. | Aerial part | 4.8 | – | Phillips et al. 2014 |
| Central America | ||||
| Agave shrevei Gentry sbsp. matapensis | Basal leaves | 21.7 | – | Laferriere et al. 1991 |
| Opuntia spp. | Cladodes | 1–10.3 | β‐carotene (2.25–53.5 mg/100 g) | Feugang et al. 2015; Rosquero Pérez 2001 |
| Opuntia ficus‐indica (L.) Mill. | Cladodes | 7.7 8.94 |
Isoquercetin (267–396.7 µg/g dw); isorharmnetin, 3, o‐glucoside (127.6–322.1 µg/g dw); nicotiflorin (317.7–1173.0 µg/g dw); rutin (147.0–261.7 µg/g dw); narcissin (567.1–1371 µg/g dw) | Granda Neri 2004’ Guevara‐Figueroa et al. 2010 |
| Opuntia leucotricha DC. | Cladodes | 7.1 | Isoquercetin (50.0 µg/g dw); isorharmnetin, 3, o‐glucoside (45.9 µg/g dw); narcissin (220.1 µg/g dw) | Guevara‐Figueroa et al. 2010 |
| Opuntia robusta Pfeiff. | Cladodes | 17.43 | Isoquercetin (106.0 µg/g dw); isorharmnetin,3,O‐glucoside (99.3 µg/g dw); nicotiflorin (910.7 µg/g dw); rutin (140.1 µg/g dw) | Guevara‐Figueroa et al. 2010; Laferriere et al. 1991 |
| Opuntia durangensis | Cladode | 16.33 | – | Laferriere et al. 1991 |
| Opuntia macrorhiza Engelm. | Cladode | 7.77 | – | Laferriere et al. 1991 |
| Opuntia lindheimeri Engelm. | Cladodes | 3.02 | – | Granda Neri 2004 |
| Opuntia imbricada (Haw.) DC. | Cladodes | 11.5 | – | Granda Neri 2004 |
| Opuntia lindheimeri var. tricolor | Cladodes | 10.7–11.4 | – | Granda Neri 2004 |
| South America | ||||
| Agave americana L. | Leaves | – | Total phenolics: 9.8–10 (mg GAE/g dw); flavonoids: 3.0–3.1 (mg QE*/g dw) | Chirino et al. 2013 |
| Alnus acuminata Kunth. | Leaves | – | Total phenolics: 71.2–73.4 (mg GAE/g dw); flavonoids: 13.11–13.63 (mg QE*/g dw), 0.28–0.30 (mg CE**/g dw) | Chirino et al. 2013 |
| Amaranthus viridis L. | Leaves | – | Total carotenoids (0.347–0.468 mg/100 g) | Mercadante & Rodriguez‐Amaya 1990 |
| Cassia hookeriana Gillies ex Hook. | Leaves | – | Total phenolics: 18.6–18.8 (mg GAE/g dw); flavonoids: 13.22–13.86 (mg QE*/g dw), 0.08 (mg CE**/g dw) | Chirino et al. 2013 |
| Cestrum auriculatum L'Hér. | Leaves | – | Total phenolics: 6.4–6.6 (mg GAE/g dw); flavonoids: 2.32–2.34 (mg QE*/g dw) | Chirino et al. 2013 |
| Clinopodium bolivianum Kuntze | Leaves | – | Total phenolics: 56.4–57.2 (mg GAE/g dw); flavonoids: 9.6–9.7(mg QE*/g dw); 1.14–1.18 (mg CE**/g dw) | Chirino et al. 2013 |
| Jungia paniculata A. Gray | Leaves | – | Total phenolics: 28.0–28.4 (mg GAE/g dw); flavonoids: 25.2–25.3(mg QE*/g dw) | Chirino et al. 2013 |
| Lepidium pseudodidymum Thell. in Druce | Leaves | – | Total carotenoids (0.237–0.280 mg/100 g) | Mercadante & Rodriguez‐Amaya 1990 |
| Lepechinia meyenii Epling | Leaves | – | Total phenolics: 60.5–61.9 (mg GAE/g dw); flavonoids: 7.7–8.2 (mg QE*/g dw) | Chirino et al. 2013 |
| Melissa officinalis L. | Leaves | – | Total phenolics: 30.7–31.7 (mg GAE/g dw); flavonoids: 4.0–4.2 (mg QE*/g dw) | Chirino et al. 2013 |
| Mutisia acuminata Ruiz & Pav. | Leaves | – | Total phenolics: 58.5–60.3 (mg GAE/g dw); flavonoids: 6.59–6.85 (mg QE*/g dw) | Chirino et al. 2013 |
| Portulaca oleracea L. | Leaves | – | Total carotenoids (0.071–0.109 mg/100 g) | Mercadante & Rodriguez‐Amaya 1990 |
| Sonchus oleraceus L. | Leaves | – | Total carotenoids (0.225–0.361 mg/100 g) | Mercadante & Rodriguez‐Amaya 1990 |
| Xanthosoma spp. | Leaves | – | Total carotenoids (0.149–0.334 mg/100 g) | Mercadante & Rodriguez‐Amaya 1990 |
| Oenothera rosea Aiton. | Leaves | – | Total phenolics: 64.5–65.9 (mg GAE/g dw); flavonoids: 26.6–26.8 (mgQE*/g dw) | Chirino et al. 2013 |
| Schimus molle L. | Leaves | – | Total phenolics: 52.1–53.3 (mg GAE/g dw); flavonoids: 11.0–11.2 (mg QE*/g dw); 8.4–8.6 (mg CE**/g dw) | Chirino et al. 2013 |
* Content of flavan‐3‐ols, flavan‐4‐ols, flavan‐3,4‐diols, flavanones, and derivatives;
** content of flavones and flavonols.
CE, catechin equivalent; dw, dry weight; GAE, gallic acid equivalent; QE, quercetin equivalent.
With regard to minerals, calcium has been found in high levels in the leaves of Chenopodium album L. and Urtica dioica (230–452 mg/100 g), reported as traditionally eaten in North America, as well as in other Central and South America species (Hedeoma patens M. E. Jones, Monarda citriodora Cerv. ex Lag. var. austromontana (Epling) B.L.Turner, Teloxys ambrosioides (L.) W. A. Weber, Trichanthera gigantea Humb. & Bonpl. ex Steud. and Xanthosoma spp.), most with levels of more than 1 g/100 g). Special attention should go to the cactus species, very popular in Central and South America, such as Agave shrevi Gentry, and cladodes of many Opuntia species, which represent a very important staple food in Mexico (even present in the arms of the country), as either wild or cultivated species. Cladodes are important calcium sources (1–2.5 mg/100 g), and the oxalate content has also been reported in some studies on cultivated Opuntia ficus‐indica L. Miller (over 1 g/100 g). Moreover, the ratio of oxalic acid/Ca is often favorable to absorption and in vitro studies about Ca bioaccessibility in cultivated Opuntia cladodes (Ramírez Moreno et al. 2011) have shown 15–50% of gut‐accessible Ca. Given the high Ca content of these vegetables, this could mean more than 150 mg/100 g of accessible Ca (even taking into account the presence of oxalates), which surpasses the daily recommendation for this mineral. For that reason, and due to its strong presence in American diets, cladodes are a valuable vegetable, except for those suffering from renal problems. As can be seen in Tables 7.3 and 7.4, Opuntia cladodes also provide high levels of Mg, Fe, and dietary fiber; this is also seen in other cacti such as Agave shrevi.
Other bioactive compounds of interest provided by traditional American plants are phenolic compounds, where flavonoids usually represent an interesting fraction (see Table 7.4), and polyunsaturated fatty acids such as α‐linolenic (C18:3n3) and linoleic (C18:2n6) acids, being the major ones in most leafy vegetables. All these compounds make these plants useful tools to improve the health status of American populations, with the added value of using their own natural resources, and for these reasons their consumption should be preserved and valued.
The largest and most diverse continent in the world is Asia, with the highest and the lowest points on the surface of the Earth, the longest coastline of any continent, and wide environmental. Consequently, it produces the most varied forms of vegetation and animal life on Earth. Using the Köppen climatic classification, Asia may be divided into three major climatic regions: Siberia (north‐east Asia), Monsoon (south‐east Asia) and Desert (west and central Asia) (Dando 2005).
Asia is a continent of contrasts – it includes developed and rich countries as Japan, but also many poor areas in developing tropical countries such as India, China, Pakistan, Iran, Thailand, etc. These countries generally have problems with food supply due to rapid population growth, shortage of land for cultivation, high prices of available staples and restrictions on the importation of food. This has resulted in a high incidence of hunger and people suffering from malnutrition (Seal 2011). Vitamin A deficiency and age‐related macular degeneration are accepted as serious public health problems among children and adults in India. It is reported that 25% of the 15 million blind in the world are from India (WHO 2000). It is known that vitamin A deficiency and age‐related macular degeneration are primarily due to inadequacy of provitamin A and macular pigments in the diet (Raju et al. 2007). Also, iron deficiency is a public health problem in developing countries because the staple foods consist mainly of rice, cereal, grains, and vegetables more than animal products (Nutrition Formulation 1982).
Since traditional medicinal plants and food are believed to share a common origin in Chinese tradition, it is very difficult to distinguish between the two. In fact, many medicinal plants have been used as flavors, pigments, and foods (Li et al. 2013). Due to the economic situation in Pakistan, India and other developing countries, the main components of the diet of the diverse ethnic groups are wild plants (Imran et al. 2009; Sundriyal & Sundriyal 2004). Nevertheless, there is still an enormous amount of plant material which has not been studied and whose nutritional composition is unknown.
Previously conducted ethnobotanical studies (Bandyopadhyay & Mukherjee 2009; Cruz‐Garcia & Price 2011; Kang et al. 2013) detail the main wild edible Asian greens discussed in this chapter. Momordica dioica Roxb., Portulaca oleracea, Centella asiatica, Commelina benghalensis L., Amaranthus spp., Chenopodium album, Urtica dioica, Ipomoea spp., Rumex spp., Dioscorea spp., and Diplazium esculentum (Retz) Sw. are widely spread in China, Thailand, Indonesia and many regions of the Arabian sea as Pakistan, India and Iran (Aberoumand & Deokule 2009; Anusuya et al. 2012; Gupta et al. 2005; Imran et al. 2009; Khattak 2011; Pradhan et al. 2015; Raghuvanshi et al. 2001; Sharifi‐Rad et al. 2014; Sultan et al. 2009; Vishwakarma & Dubey 2011).
Vitamins and minerals present in 100 g of plant with a higher content than 15% of the daily recommendations of nutrients given by the FNB (Trumbo et al. 2002) or FAO/WHO (2004) are shown in Table 7.5. Generally, these wild greens have a high mineral content, iron being the main element. Some Asian wild edible plants could provide 100% of the daily recommendation of iron (9 mg/100 g), such as Portulaca oleracea, Amaranthus spp., Centella asiatica, Sonchus arvensis L., and Digera arvensis Forsk. (see Table 7.5). Public health problems related to Fe deficiency, such as anemia, could be palliated by including these wild greens in the diet of at‐risk populations.
Table 7.5 Vegetables traditionally consumed in Asia, standing out as sources of vitamins or minerals. Data are given per 100 g of fresh weight.
| Species | Edible part | Vitamins | Minerals | References |
| Amaranthus spp. | Leaves | Vitamin C (39–44 mg/100 g) | K (382–433 mg/100 g); Ca (239 mg/100 g); Mg (253 mg/100 g); Fe (5.8–15 mg/100 g); Cu (1.1 mg/100 g); Cr (140 µg/100 g) | Gupta et al. 2005; Lata et al. 2011; Pradhan et al. 2015 |
| Bauhenia purpurea L. | Leaves | Vitamin B1 (0.1 mg/100 g); B3 (0.87 mg/100 g); C (173 mg/100 g) | Ca (156 mg/100 g); Fe (4.6 mg/100 g) | Raghuvanshi et al. 2001 |
| Boerhaavia diffusa L. | Leaves | Vitamin C (16 mg/100 g) | Ca (330 mg/100 g); Mg (167 mg/100 g); Fe (7.8 mg/100 g) | Gupta et al. 2005 |
| Brassica campestris L. | Leaves | Vitamin C (51 mg/100 g) | Mg (59 mg/100 g); Fe (5.7 mg/100 g); Cu (1.1 mg/100 g); Mn (12.1 mg/100 g); Zn (3.3 mg/100 g) | Khattak 2011 |
| Celosia argentea L. | Leaves | Vitamin C (26 mg/100 g) | K (476 mg/100 g); Ca (188 mg/100 g); Mg (233 mg/100 g); Fe (13.1 mg/100 g); Cu (0.15 mg/100 g) and Cr (153 µg/100 g) | Gupta et al. 2005 |
| Centella asiatica L. Urb. | Leaves | – | K (345 mg/100 g); Ca (174–208 mg/100 g); Mg (87 mg/100 g); Fe (4.2–15.9 mg/100 g); Cu (0.24 mg/100 g) | Gupta et al. 2005; Lata et al. 2011; Ogle et al. 2001 |
| Chenopodium album L. | Leaves | Vitamin B3 (0.71 mg/100 g); C (33.6–43.7 mg/100 g) | K (848 mg/100 g); Ca (155.7–265 mg/100 g); Mg (112 mg/100 g); Fe (4.7–5.4 mg/100 g); Cu (0.47–1.22 mg/100 g); Mn (0.9 mg/100 g); Zn (1.3–8.4 mg/100 g) | Katach et al. 2011; Lata et al. 2011; Pradhan et al. 2015; Raghuvanshi et al. 2001; Sultan et al. 2009 |
| Cicer arietinum L. | Leaves and young shoots | Vitamin C (105 mg/100 g) | Mg (140 mg/100 g); Fe (8.4 mg/100 g); Cu (1.5 mg/100 g); Mn (8.5 mg/100 g); Zn (3.5 mg/100 g) | Khattak 2011 |
| Clerodendrum colebrookianum Walp. | Leaves | – | Ca (857 mg/100 g); Fe (69.7 mg/100 g); Cu (0.76 mg/100 g); Mn (8.6 mg/100 g); Zn (8.3 mg/100 g) | Seal et al. 2011 |
| Cocculus hirsutus (L.) Diels. | Leaves | Vitamin C (28 mg/100 g); B1 (0.19 mg/100 g) | K (343 mg/100 g); Mg (35 mg/100 g); Fe (9.9 mg/100 g); Cu (0.22 mg/100 g) | Gupta et al. 2005 |
| Coleus aromaticus Benth. | Leaves | – | Ca (158 mg/100 g); Mg (88 mg/100 g); Fe (2.62 mg/100 g) | Gupta et al. 2005 |
| Commelina benghalensis L. | Leaves | Vitamin C (46 mg/100 g) | K (473 mg/100 g); Mg (77 mg/100 g); Fe (2.5–7.1 mg/100 g); Cr (115 µg/100 g) | Gupta et al. 2005; Lata et al. 2011 |
| Cucurbita maxima | Leaves | Vitamin B1 (0.20 mg/100 g); C (37 mg/100 g) | K (368 mg/100 g); Ca (302 mg/100 g); Mg (150 mg/100 g); Fe (4.4 mg/100 g); Cu (0.19 mg/100 g); Cr (49 µg/100 g) | Gupta et al. 2005 |
| Delonix elata (L.) Gamble | Leaves | Vitamin B1 (0.33 mg/100 g); C (295 mg/100 g) | K (365 mg/100 g); Mg (59 mg/100 g); Fe (6.2 mg/100 g); Cu (0.27 mg/100 g); Cr (68 µg/100 g) | Gupta et al. 2005 |
| Digera arvensis Forssk. | Leaves | Vitamin C (49 mg/100 g) | K (604 mg/100 g); Ca (506 mg/100 g); Mg (232 mg/100 g); Fe (17.7 mg/100 g); Cu (0.16 mg/100 g) | Gupta et al. 2005 |
| Dioscorea spp. | Shoots | – | K (360 mg/100 g); Ca (191 mg/100 g); Mg (42.6–179 mg/100 g); Fe (2.7–5.2 mg/100 g); Cu (0.16–1.39 mg/100 g); Mn (0.59–0.97 mg/100 g) | Shanthakumari et al. 2008 |
| Diplazium esculentum (Retz.) Sw. | Leaves | Vitamin B9 (630 µg/100 g); C (21.0–21.7 mg/100 g) | Ca (193 mg/100 g); Fe (11.2 mg/100 g); Cu (0.32 mg/100 g); Zn (2.7 mg/100 g) | Irawan et al. 2006; Pradhan et al. 2015 |
| Fagopyrum esculentum Moench. | Leaves | Vitamin B2 (0.24 mg/100 g); C (84.9 mg/100 g) | Ca (355 mg/100 g); Fe (6.2 mg/100 g) | Raghuvanshi et al. 2001 |
| Gynandropsis penthaphylla (L.) DC. | Leaves | Vitamin B1 (0.16 mg/100 g); C (42 mg/100 g) | K (360 mg/100 g); Ca (151 mg/100 g); Mg (77 mg/100 g); Fe (4.8 mg/100 g) | Gupta et al. 2005 |
| Ipomoea aquatica Forssk. | Leaves | RE (700 µg/100 g) | Fe (1.5–4.0 mg/100 g) | Lata et al. 2011; Ogle et al. 2001; |
| Nasturtium officinale W.T. Aiton | Leaves | Vitamin C (13 mg/100 g) | Fe (7 mg/100 g); Cu (0.58 mg/100 g); Zn (2.0 mg/100 g) | Pradhan et al. 2015 |
| Polygala erioptera DC. | Leaves | Vitamin C (85 mg/100 g) | Mg (57 mg/100 g); Fe (4.8 mg/100 g); Cu (0.15 mg/100 g) | Gupta et al. 2005 |
| Portulaca oleracea L. | Leaves | Vitamin C (50.6 mg/100 g) | Mg (87 mg/100 g); Fe (4.5–29.7 mg/100 g); Cu (2.3 mg/100 g); Mn (8.6 mg/100 g); Zn (4.7 mg/100 g) | Khattak 2011; Lata et al. 2011; Ogle et al. 2001 |
| Rumex spp. | Leaves | – | Zn (1.7 mg/100 g) | Anusuya et al. 2012; Sharifi‐Rad et al. 2014 |
| Sonchus arvensis L. | Leaves | – | Ca (918 mg/100 g); Fe (26.0 mg/100 g); Cu (0.56 mg/100 g); Mn (1 mg/100 g); Zn (8.0 mg/100 g) | Seal et al. 2011 |
| Thrianthema portulacastrum L. | Leaves | Vitamin C (22 mg/100 g) | K (317 mg/100 g); Mg (153 mg/100 g); Fe (4.2 mg/100 g); Mn (0.43 mg/100 g) | Gupta et al. 2005 |
| Urtica dioica L. | Leaves | – | K (917 mg/100 g); Ca (244 mg/100 g); Fe (8.1 mg/100 g); Cu (0.43–0.67 mg/100 g); Zn (2.3 mg/100 g) | Pradhan et al. 2015; Sultan et al. 2009 |
RE, retinol equivalent.
Also, these Asian wild leafy vegetables have an important vitamin C content. The daily recommendation for vitamin C reported by FAO/WHO (2004) is 45 mg/100 g. Cicer arietinum L. leaves contain twice the daily recommendation of vitamin C for adults, and Delonix elata Gamble stands out for its high vitamin C content. These plants also have good fiber content (Table 7.6), Cocculus hirsutus L. (Diels.) having the highest levels.
Table 7.6 Vegetables traditionally consumed in Asia, standing out as sources of bioactive compounds. Data are given per 100 g of fresh weight.
| Species | Edible part | Dietary fiber (g/100 g) | Carotenoids/PUFA/organic acids/phenolics/others | References |
| Amaranthus spp. | Leaves | 4.8 | β‐carotene (5410 µg/100 g); total oxalates (1270 mg/100 g); soluble oxalates (690 mg/100 g); phytic acid (1.9 mg/100 g); total phenolics (9800 mg GAE/100 g) | Gupta et al. 2005; Pradhan et al. 2015 |
| Bambusa balcooa Roxb. | Shoots | – | Organic acids (0.1 mg/100 g); lactic acid (282 mg/100 g); piruvic acid (3.7 mg/100 g); tartaric acid (173 mg/100 g); total phenolics (97.5 catechin equivalents) | Badwaik et al. 2014 |
| Bauhenia purpurea L. | Leaves | 5.0 | β‐carotene (1302 µg/100 g); oxalic acid (356 mg/100 g); phytic acid (35.6 mg/100 g) | Raghuvanshi et al. 2001 |
| Boerhaavia diffusa L. | Leaves | 7.3 | β‐carotene (6730 µg/100 g); total oxalates (1250 mg/100 g); soluble oxalates (420 mg/100 g); phytic acid (4.1 mg/100 g) | Gupta et al. 2005 |
| Brassica campestris L. | Leaves | – | Total phenolics (18900 mg/100 g) | Khattak 2011 |
| Celosia argentea L. | Leaves | 5.1 | β‐carotene (4420 µg/100 g); total oxalates (920 mg/100 g); soluble oxalates (580 mg/100 g); phytic acid (2.9 mg/100 g) | Gupta et al. 2005 |
| Centella asiatica L. Urb. | Leaves | 4.1–5.9 | β‐carotene (3341–3900 µg/100 g); RE (564/100 g); total oxalates (60 mg/100 g); soluble oxalates (20 mg/100 g); phytic acid (2.1 mg/100 g) | Gupta et al. 2005; Lata et al. 2011; Ogle et al. 2001 |
| Chenopodium album L. | Leaves | – | β‐carotene (1838 µg/100 g); oxalic acid (142 mg/100 g); phytic acid (5.1 mg/100 g); total phenolics (2916–9800 mg GAE/100 g); phenolic acids (6.98 mg/100 g) | Khattak 2011; Pradhan et al. 2015 ; Raghuvanshi et al. 2001 |
| Cocculus hirsutus (L.) Diels. | Leaves | 11.1 | β‐carotene (9200 µg/100 g); total oxalates (230 mg/100 g); soluble oxalates (140 mg/100 g); phytic acid (2.4 mg/100 g) | Gupta et al. 2005 |
| Coleus aromaticus Benth. | Leaves | – | β‐carotene (1500 µg/100 g); total oxalates (50 mg/100 g); soluble oxalates (20 mg/100 g); phytic acid (0.92 mg/100 g) | Gupta et al. 2005 |
| Commelina benghalensis L. | Leaves | 1.5–5.4 | β‐carotene (3810 µg/100 g); total oxalates (390 mg/100 g); soluble oxalates (40 mg/100 g); phytic acid (4.4 mg/100 g) | Gupta et al. 2005; Lata et al. 2011 |
| Cucurbita maxima Duchesne in Lam. | Leaves | 5.8 | β‐carotene (2270 µg/100 g); total oxalates (200 mg/100 g); soluble oxalates (70 mg/100 g); phytic acid (9.2 mg/100 g) | Gupta et al. 2005 |
| Delonix elata (L.) Gamble | Leaves | 8.8 | β‐carotene (10510 µg/100 g); total oxalates (90 mg/100 g); soluble oxalates (30 mg/100 g); phytic acid (5.1 mg/100 g) | Gupta et al. 2005 |
| Digera arvensis Forssk. | Leaves | 4.4 | β‐carotene (3360 µg/100 g); total oxalates (1410 mg/100 g); soluble oxalates (570 mg/100 g); phytic acid (2.5 mg/100 g) | Gupta et al. 2005 |
| Dioscorea spp. | Shoots | – | Total oxalates (1.9–79.8 mg/100 g); total phenolics (14.6–105.3 mg /100 g) | Mohan & Kalidass 2010; Shanthakumari et al. 2008 |
| Diplazium esculentum (Retz.) Sw. | Leaves | 4.8 | Total phenolics (6800 mg GAE/100 g) | Irawan et al. 2006; Pradhan et al. 2015 |
| Fagopyrum esculentum Moench. | Leaves | – | β‐carotene (3020 µg/100 g); oxalic acid (316 mg/100 g); phytic acid (5.3 mg/100 g) | Raghuvanshi et al. 2001 |
| Gynandropsis penthaphylla (L.) DC. | Leaves | 3.3 | β‐carotene (5380 µg/100 g); total oxalates (20 mg/100 g); soluble oxalates (10 mg/100 g); phytic acid (13.1 mg/100 g) | Gupta et al. 2005 |
| Ipomoea aquatica Forssk. | Leaves | 3.2 | β‐carotene (4164 µg/100 g) | Lata et al. 2011; Ogle et al. 2001 |
| Malcomia africana (L.) R. Br. | Leaves | – | PUFA (61.2%); C18:3n3 (38.3%); C18:2n6 (9.2%) | Imran et al. 2009 |
| Mentha longifolia (L.) Huds. | Leaves | – | PUFA (33.5%); C18:3n3 (18.0%); linoleic acid (15.5%) | Imran et al. 2009 |
| Nasturtium officinale W.T. Aiton | Leaves | – | Total phenolics (1800 mg GAE/100 g) | Pradhan et al. 2015 |
| Polygala erioptera DC. | Leaves | 6.6 | β‐carotene (3830 µg/100 g); total oxalates (60 mg/100 g); soluble oxalates (10 mg/100 g); phytic acid (3.4 mg/100 g) | Gupta et al. 2005 |
| Portulaca oleracea L. | Leaves | 5.22 | Total carotenoids (2234 mg/100 g); PUFA (48.5%); C18:3n6 (30.1%); C18:2n6 (18.5%) | Katach et al. 2011 ; Imran et al. 2009 |
| Spinacia oleracea L. | Leaves | – | PUFA (52.4%); C18:3n3 (43.4%); C18:2n6 (9%) | Imran et al. 2009 |
| Stellaria media (L.) Vill. | Leaves | – | PUFA (33.7%); C18:3n3 (21.4%); C18:2n6 (12.2%) | Imran et al. 2009 |
| Thrianthema portulacastrum L. | Leaves | – | β‐carotene (4000 µg/100 g); total oxalates (1080 mg/100 g); soluble oxalates (610 mg/100 g); phytic acid (2.0 mg/100 g) | Gupta et al. 2005 |
| Urtica dioica L. | Leaves | – | PUFA (47.5%); linolenic acid (45.5%); linoleic acid (15.7%); total phenolics (17 600 mg GAE/100 g) | Imran et al. 2009; Pradhan et al. 2015 |
GAE, gallic acid equivalent; PUFA, polyunsaturated fatty acid.
Some plants contain linoleic, linolenic, and palmitic acid as the main fatty acids (see Table 7.6). The main carotenoid in all the plants was β‐carotene (see Table 7.6). Regarding antinutrients, Digera arvensis presents the highest total oxalate content and Gynandropsis penthaphylla (L.) DC. the highest phytic acid content (13.1 mg/100 g).
These plants are a good resource of food to combat hunger and important diseases in developing countries.
Since the nineteenth century, socioeconomic progress and public health measures in Europe have lead to increased life expectancy, mainly as result of reduced mortality in early life. Mackenbach et al. (2008) found that inequalities in mortality rates are smaller in some southern European countries but very large in most countries in the eastern and Baltic regions. The WHO European Region has seen remarkable health gains arising from progressive improvements in the conditions in which people are born, grow, live, and work. However, levels of health vary significantly between countries. These differences are even greater when inequities within countries, according to gender and socioeconomic position, are considered (Groenewold et al. 2008; WHO 2013).
Chronic diseases are the leading cause of mortality and morbidity in Europe, and research suggests that complex conditions such as cardiovascular disease, diabetes, asthma, and chronic obstructive pulmonary disease (COPD) will mean a greater burden in the future. Many of these are connected to an aging society but also to lifestyle choices such as smoking, sexual behavior, diet, and exercise, as well as genetic predispositions (Busse et al. 2010).
In recent decades, public health research has focused on proximate causes of health and health inequities. The European Commission has developed an action plan for dietary guidelines based on existing evidence from health promotion programmes. The plan describes population goals in terms of nutrients and lifestyle for the prevention of chronic diseases in Europe (Busse et al. 2010). Therefore, in recent decades, dietary guidelines and healthy food consumption have been promoted to reduce the risk and manage chronic diseases. The combination of consumer requirements, food technology advances, and the improvement in evidence‐based science concerning diet and disease prevention has created an important opportunity to address public health issues through diet and lifestyle. Widespread interest in foods that might promote health has lead to use of the term “functional foods.” Many researchers have provided evidence of the clear relationships between dietary components and health benefits (Clydesdale 2005). In the case of traditional wild vegetables, despite current lifestyles and eating habits which make their use difficult, there is growing scientific interest in the potential benefits of these vegetables for their nutritional properties and the wealth of bioactive compounds, such as antioxidants, which have proven health‐promoting properties (Burton & Traber 1990; Carpenter et al. 2009; Pardo de Santayana et al. 2010).
Wild plant gathering has been a habitual practice from ancient times in Europe, especially in times of shortage, playing an important role in complementing and balancing a diet based on agricultural foods. Many species now considered as weeds were considered food in past times. Nowadays, in our society many of these species have been forgotten, even when they have an important nutritive value, though many plant species are still used in other countries. However, some agricultural populations include significant quantities of forage plants in their diets and they are much appreciated, often being sold in local markets (Ertug 2004). Moreover, edible wild plants are considered essential elements of many European cultures and are a predominant feature of the landscape created by humans over the centuries (Heinrich et al. 2006a,b).
Many European ethnobotanical studies have reported on traditional knowledge about the plants used, most of them focused in the Mediterranean countries (Hadjichambis et al. 2008; Leonti et al. 2006; Sánchez‐Mata & Tardío, 2016; Tardío et al. 2006). These species can be very valuable during seasons when fresh agricultural products are scarce, such as winter and spring in the case of wild vegetables.
In recent years, many authors have undertaken the characterization of different chemical compounds in order to assess the nutritional potential of these wild species that have been part of the traditional diet of our ancestors and are still present in our current diet (Tables 7.7 and 7.8) (Barros et al. 2009, 2010a,b,c, 2011a,b; Conforti et al. 2008, 2011; Dias et al. 2013, 2014; García Herrera et al. 2014a,b; Guil et al. 1996a,b, 1997a,b,c, 1998, 2003; Hinneburg et al. 2006; Martins et al. 2011; Morales et al. 2012a,b, 2014, 2015; Sánchez‐Mata et al. 2012; Pereria et al. 2011, 2013; Salvatore et al. 2005; Tardío et al. 2011; Trichopoulou et al. 2000; Vasilopoulo et al. 2011; Vardavas et al. 2006a,b, among many others). Also, it is important to keep in mind the great variability of these wild species, and in many cases indigenous varieties differ from species harvested and consumed in other countries.
Table 7.7 Vegetables traditionally consumed in Europe, standing out as sources of vitamins or minerals. Data are given per 100 g of fresh weight.
| Species | Edible part | Vitamins | Minerals | References |
| Allium ampeloprasum L. | Bulbs and pseudostem | Vitamin B9 (100–190 µg/100 g) | K (145–600 mg/100 g); Cu (0.04–0.18 mg/100 g) | García Herrera et al. 2014a Morales et al. 2015 |
| Anchusa azurea Mill. | Leaves | Vitamin B9 (256–299 µg/100 g); C (5.41–18.11 mg/100 g) | Ca (126–219 mg/100 g); K (268–1172 mg/100 g); Mn (0.15–0.699 mg/100 g) | Ayan et al. 2006; Morales et al. 2012; García Herrera et al. 2014b; Morales et al. 2015 |
| Apium nodiflorum (L.) Lag. | Young leaves and stems | Vitamin B9 (125 µg/100 g); C (10.3–30.2 mg/100 g); E* (2.62 mg/100 g); | Ca (152 mg/100 g); Cu (0.08 mg/100 g) | Morales 2012; Morales et al. 2012; García Herrera et al. 2014; Morales et al. 2015 |
| Asparagus acutifolius L. | Young shoots | Vitamin B9 (217 µg/100 g); C (37.8 mg/100 g); E (8.21 mg/100 g) | K (492–1370 mg/100 g); Mg (17–109 mg/100 g); Mn (0.410 mg/100 g) | Bianco et al. 1996; Martins et al. 2011; Romojaro et al. 2013; Gárcia Herrera 2014; Morales 2012; Morales et al. 2015 |
| Beta maritima L. | Leaves | Vitamin B9 (309 µg/100 g); C (18.3–66 mg/100 g) | K (540–2356 mg/100 g); Fe (1.42–4.31 mg/100 g); Mg (13.2–135 mg/100 g); Mn (0.640–1.260 mg/100 g) | Guil et al. 1997a,b; Sánchez‐Mata et al. 2012; García Herrera 2014; Morales et al. 2014; Morales et al. 2015 |
| Borago officinalis L. | Leaves | RAE** (238 µg/100 g) | K (567 mg/100 g); Ca (344 mg/100 g) | Bianco et al. 1996; Salvatore et al. 2005 |
| Bryonia dioica Jacq. | Young shoots | Vitamin B9 (43.2 µg/100 g); C (21.4 mg/100 g); K (95 µg/100 g); E (2.64 mg/100 g) | K (487 mg/100 g); Cu (0.220 mg/100 g); Mn (0.250 mg/100 g) | Vardavas et al. 2006a,b; Martins et al. 2011; Morales et al. 2012; 2015; Sanchez‐Mata et al. 2012; Gárcia Herrera 2014; García Herrera et al. 2014 |
| Capsella bursa‐pastoris (L.) Medik. | Leaves | Vitamin C (91–169 mg/100 g) | K (315–564 mg/100 g); Ca (115–203 mg/100 g); Fe (3.50–6.14 mg/100 g); Mn (0.670–1.110 mg/100 g) | Gui‐Guerrero et al. 1999b; Ayan et al. 2006; Kiliç and Cpskun 2007 |
| Chenopodium album L. | Leaves | Vitamin C (137–171 mg/100 g) | K (855–1444 mg/100 g); Ca (236–438 mg/100 g); Mg (112–393 mg/100 g); Fe (4.79–5.80 mg/100 g); Cu (0.040–0.330 mg/100 g); Mn (0.550–1.590 mg/100 g) | Aliotta and Pollio 1981; Guil‐Guerrero et al. 1997a; Guil‐Guerrero and Torija‐isasa 1997; Bianco et al. 1998; Yildrim et al. 2001 |
| Chondrilla juncea L. | Leaves | Vitamin B9 (90.2 µg/100 g) | K (433–1277 mg/100 g); Mn (970 µg/100 g); Ca (22–472 mg/100 g); Mg (2.70–100 mg/100 g); Cu (0.430 mg/100 g); Zn (1.630 mg/100 g) | Morales et al. 2012b; 2015; Ranfa et al. 2014; García Herrera et al. 2014b |
| Cichorium intybus L. | Leaves | Vitamin B9 (253 µg/100 g); C (11.5–23 mg/100 g); K (173 mg/100 g); RAE (245 µg/100 g) | K (50–1085 mg/100 g); Ca (45.5–276 mg/100 g) | Bianco et al. 1998; Vardavas et al. 2006b; Sánchez‐Mata et al. 2012; García Herrera et al. 2014b; Morales et al. 2014; 2015 |
| Crithmum maritimum L. | Leaves | Vitamin C (39–76.6 mg/100 g) | Mg (57.4–97 mg/100 g); Mn (432–1080 mg/100 g); Ca (85–414 mg/100 g); Fe (1.09–3.70 mg/100 g) | Franke 1982; Guil‐Guerrero et al. 1996a; 1997a; 1998b; Romojaro et al. 2013 |
| Daucus carota L. | Leaves | Vitamin C (127 mg/100 g); K (328 µg/100 g) | – | Vardavas et al. 2006a, b |
| Eruca vesicaria (L.) Cav. | Leaves | Vitamin C (125 mg/ 00 g); E (3.08 mg/100 g); K (31 µg/100 g) | Ca (160–327 mg/100 g); Mg (22–48.1 mg/100 g); Fe (1.04–2.91 mg/100 g) | Bianco et al. 1998; Vardavas et al. 2006b; Villatoro et al. 2012 |
| Foeniculum vulgare Mill. | Leaves | Vitamin B9 (271 µg/100 g); C (18–101 mg/100 g) | K (674 mg/100 g dw); Ca (1272 mg/100 g dw); Mg (235.9 mg/100 g dw); Fe (0.07–10.2 mg/100 g dw); Zn (0.33 mg/100 g dw) | Trichopoulou et al. 2000; Zeguichi et al. 2003; Vardavas et al. 2006b; Conforti et al. 2009; Morales et al. 2012a; 2015; Sánchez‐Mata et al. 2012; Romojaro et al. 2013; García Herrera et al. 2014 |
| Fragaria vesca L. | Roots and vegetative parts | Vitamin B9 (115 µg/100 g); E (3.3 mg/100 g) | K (237–2774 mg/100 g); Ca (196–822 mg/100 g); Mg (30.4–331 mg/100 g); Fe (45.3 mg/100 g); Zn (0.799 mg/100 g) | Dias et al. 2015 |
| Humulus lupulus L. | Young shoots | Vitamin B9 (144 µg/100 g); C (28.6–61.1 mg/100 g) | K (314–675 mg/100 g); Mg (32.5 mg/100 g) | Morales 2012; Morales et al. 2012a; 2015; Sánchez‐Mata et al. 2012; García Herrera et al. 2013; García Herrera 2014 |
| Malva sylvestris L. | Leaves | Vitamin C (72–178 mg/100 g); E (20.58 mg/100 g) | K (547–836 mg/100 g); Ca (122–361 mg/100 g); Mg (209–368 mg/100 g); Fe (0.76–6.29 mg/100 g); Cu (0.10–0.330 mg/100 g); Mn (0.203–0.760 mg/100 g); Zn (0.038–2.665 mg/100 g) | Franke & Hensbook 1981; Guil et al. 1997a,b; 1999a; Hiçsomenez et al. 2009; Barros et al. 2010a; Romojaro et al. 2013 |
| Montia fontana L. | Young leaves and stems | Vitamin B9 (41.8 µg/100 g); C (28.9–39.7 mg/100 g); E (4.62 mg/100 g) | K (356 mg/100 g); Mn (1070 mg/100 g) | Pereira et al. 2011; Morales 2012; Tardío et al. 2011; Morales et al. 2012a,b; 2015 |
| Papaver rhoeas L. | Young leaves and stems | Vitamin B9 (152 µg/100 g); C (18.7–47.6 mg/100 g); K (145 µg/100 g) | K (188–1672 mg/100 g); Cu (0.130–1.070 mg/100 g); Mn (0.390–1.060 mg/100 g) | Bianco et al. 1998; Trichopulou et al. 2000; Vardavas et al. 2006a; Sánchez‐Mata et al. 2012; García Herrera 2014; Morales et al. 2014; 2015 |
| Plantago lanceolata L. | Leaves | Vitamin C (13.6 mg/100 g) | K (263–415 mg/100 g); Ca (57–660 mg/100 g); Mg (20.7–88 mg/100 g); Fe (1.11–5.12 mg/100 g); Cu (0.090–0.190 mg/100 g); Mn (0.310–1.012 mg/100 g) | Guil‐Guerrero et al. 2001; Queralt et al. 2005; Ayan et al. 2006 |
| Plantago major L. | Leaves | Vitamin C (24.3–92 mg/100 g) | K (283–357 mg/100 g); Mg (81–109 mg/100 g); Fe (1.20–2.80 mg/100 g); Cu (0.100–0.230 mg/100 g); Mn (0.300–0.520 mg/100 g) | Franke & Hensbook 1981; Aliotta and Pollio 1981; Guil‐Guerrero et al. 1998b; Guil‐Guerrero et al. 2001; Stef et al. 2010 |
| Portulaca oleracea L. | Leaves | Vitamin C (29–109 mg/100 g) | K (280–611 mg/100 g); Mg (56–276 mg/100 g); Fe (2.90–5.68 mg/100 g); Cu (0.360–0.420 mg/100 g); Mn (0.540–0.640 mg/100 g) | Bruno et al. 1980; Franke & Hensbook 1981; Guil‐Guerrero et al. 1997a; Bianco et al. 1998; Dias et al. 2009 |
| Prasium majus L. | Leaves | Vitamin K (373 µg/100 g) | – | Vardavas et al. 2006a |
| Rumex obtusifolius L. | Leaves | Vitamin C (32 mg/100 g); K (328 µg/100 g) | – | Vardavas et al. 2006a |
| Rumex papillaris Boiss. & Reut. | Leaves | Vitamin B9 (187 µg/100 g); C (18.9–32.3 mg/100 g) | K (351 mg/100 g); Mg (45 mg/100 g); Mn (0.750 mg/100 g) | Morales et al. 2012b; 2014; 2015; Sánchez‐Mata et al. 2012; García Herrera 2014 |
| Rumex pulcher L. | Leaves | Vitamin B9 (478 µg/100 g); C (28.7–46.5 mg/100 g) | K (891 mg/100 g) | Morales et al. 2014; 2015; Sánchez‐Mata et al. 2012; García Herrera 2014 |
| Scolymus hispanicus L. | Peeled basal leaves | Vitamin B9 (103 µg/100 g); K (38 µg/100 g); RAE (8.08 µg/100 g) | K (1040 mg/100 g); Ca (235 mg/100 g); Fe (2.36 mg/100 g) | Vardavas et al. 2006; Morales et al. 2012; 2014; 2015; Sánchez‐Mata et al. 2012; García Herrera et al. 2014b |
| Silene vulgaris (Moench.) Garcke | Young leaves and stems | Vitamin B9 (267 µg/100 g); C (25.5 mg/100 g); K (172 µg/100 g); RAE (85.7 µg/100 g) | K (601 mg/100 g); Ca (70.7–254 mg/100 g); Mg (24.2–109 mg/100 g); Mn (0.540–1.010 mg/100 g) | Zeguichi et al. 2003; Alarcón et al. 2006; Ayan et al. 2006; Vardavas et al. 2006; Morales 2012; Morales et al. 2012; 2015; Egea‐Gilabert et al. 2013; García Herrera 2014 |
| Silybum marianum (L.) Gaertner | Peeled basal leaves | Vitamin B9 (41.7 µg/100 g) | K (718 mg/100 g) | Bianco et al. 1998; Morales et al. 2012; 2015; Sánchez‐Mata et al. 2012; García Herrera et al. 2014 |
| Smilax aspera L. | Leaves | Vitamin E (29.1 mg/100 g) | Mg (61.2 mg/100 g); Fe (1.01–2.31 mg/100 g) | Demo et al. 1998; Cabiddu & Decandia 2000; Poschenrieder et al. 2012 |
| Sonchus asper (L.) Hill | Basal leaves and stems | Vitamin C (62.8 mg/100 g) | K (511 mg/100 g); Fe (2.98 mg/100 g); Mn (880 µg/100 g) | Bianco et al. 1998; Guerrero‐Guil et al. 1998a |
| Sonchus oleraceus L. | Leaves | Vitamin B9 (85.9 µg/100 g); C (10.1–86 mg/100 g); K (175 µg/100 g); RAE (87.5 µg/100 g) | K (481 mg/100 g); Ca (32–280 mg/100 g); Fe (0.57–5.62 mg/100 g); Mn (0.370–1.269 mg/100 g) | Saleh et al. 1977; Bruno et al. 1980; Guil‐Guerrero et al. 1996b; 1997a; Bianco et al. 1998; Zeghichi et al. 2003; Ayan et al. 2006; Vardavas et al. 2006b; García Herrera et al. 2014b; Morales et al. 2014; 2015 |
| Tamus communis L. | Young shoots | Vitamin B9 (381 µg/100 g); C (58.6–79.4 mg/100 g) | K (371 mg/100 g); Ca (47 mg/100 g); Mg (22.4 mg/100 g); Cu (0.130 mg/100 g); Mn (0.165 mg/100 g) | Barros et al. 2011b; Martins et al. 2011, Morales 2012; Morales et al. 2012a, b; Sánchez‐Mata et al. 2012; Pereira et al. 2013; García Herrera et al. 2013; García Herrera 2014 |
| Taraxacum officinale Weber | Leaves | Vitamin C (8.00–62.2 mg/100 g) | Fe (0.34–14.4 mg/100 g); Mn (0.699 mg/100 g) | Aliotta & Pollio 1981; Bockholt & Schnittke 1996; Bianco et al. 1998; Ayan et al. 2006; Gjorgieva et al. 2010; Gatto et al. 2011; Dias et al. 2014 |
| Taraxacum obovatum (Willd.) DC. | Leaves | Vitamin B9 (110 µg/100 g); C (11.5–20.8 mg/100 g) | K (566 mg/100 g); Ca (177 mg/100 g); Fe (3.57 mg/100 g); Cu (0.150 mg/100 g) | García Herrera et al. 2014b; Morales et al. 2014 |
| Urtica dioica L. | Leaves | Vitamin B2 (230 µg/100 g); B3 (620 µg/100 g); C (238–333 mg/100 g); RAE (476 µg/100 g) | K (13.3–740 mg/100 g); Ca (246–982 mg/100 g); Mg (14–482 mg/100 g); Cu (0.100–0.502 mg/100 g) | Kudritsata & Zagorodskaya 1987; Wetherilt 1992; Bianco et al. 1998; Guil‐Guerrero et al. 2003 |
* Vitamin E: calculated as content of α‐tocopherol + (content of β‐tocopherol/2) + (content of γ‐tocopherol/10) + (content of δ‐tocopherol/30).
** RAE (= retinol activity equivalents) are usually calculated as (content of β‐carotene/12) + (contents of other provitamin A carotenoids /24); according to Mahan et al. (2012).
Table 7.8 Vegetables traditionally consumed in Europe, standing out as sources of bioactive compounds. Data are given per 100 g of fresh weight.
| Species | Edible part | Fiber (g/100 g) | Carotenoids/tocopherols/PUFA/organic acids/phenolics/others | References |
| Allium ampeloprasum L. | Bulbs and pseudostem | 3.72–4.74 | Total phenolic compounds (42.2 mg GAE/g extract), total flavonoids (6.30 mg CE/g extract) | García Herrera et al. 2014a; Morales et al. 2015 |
| Achillea millefolium L. | Vegetative part | – | γ‐tocopherol (13.04 mg/100 g dw); C18:2n6 (47.16%); total phenolic acids (103.80 mg/g extract); total flavonoids (24.56 mg/g extract); total phenolic compounds (128.36 mg/g extract) | Dias et al. 2013 |
| Anchusa azurea Mill. | Leaves | 3.50–4.40 | PUFA and n‐3 proportion (80.4 and 67.9%); oxalic acid (110–640 mg/100 g); total phenolic compounds (148 mg GAE/g extract; 178 mg chlorogenic acid/g); total flavonoids (84.8 mg CE/g extract) | Ayan et al. 2006; Conforti et al. 2011; García Herrera et al. 2014b; Morales et al. 2014 |
| Apium nodiflorum (L.) Lag. | Young leaves and stems | – | α‐tocopherol (2.59 mg/100 g); oxalic acid (189–879 mg/100 g); total phenolics (80.5 mg GAE/g extract); total flavonoids (45.5 mg CE/g extract) | Morales 2012; Morales et al. 2012a |
| Asparagus acutifolius L. | Young shoots | 4.83 | α‐tocopherol (7.88 mg/100 g); citric acid content (308 mg/100 g); total phenolics (17.6 mg GAE/g extract; 265 mg/g); phenolic acids (6.09 mg caffeic acid/g); total flavonoids (6.09 mg CE/g extract; 30 mg/g; 226 mg QE/g) | Bianco et al. 1996; Barros et al., 2011b; Martins et al. 2011; Morales 2012; Romojaro et al. 2013; Gárcia Herrera 2014; Morales et al. 2014 |
| Beta maritima L. | Leaves | 3.29–9.50 | Oxalic acid (50–1070 mg/100 g); total phenolics (61.9 mg GAE/g extract); total flavonoids (21.5 mg CE/g extract) | Guil et al. 1997a; Sánchez‐Mata et al. 2012; García Herrera 2014; Morales et al. 2014 |
| Borago officinalis L. | Leaves | – | β‐carotene (2.86 mg/100 g); lutein (3.81 mg/100 g); neoxanthin (1.13 mg/100 g); violaxanthin (1.15 mg/100 g); α‐tocopherol (1.08–1.22 mg/100 g); oxalic acid (561–569 mg/100 g); total phenolics (39.6 mg/g); phenolic acids (6.40 mg caffeic acid/g); total flavonoids (18.9 mg QE/g) | Salvatore et al. 2005; Gatto et al. 2011; Pereira et al. 2011; 2013 |
| Bryonia dioica Jacq. | Young shoots | 4.60 | β‐carotene (0.15–1.95 mg/100 g); lutein (0.68–3.70 mg/100 g); neoxanthin (0.17–3.70 mg/100 g); violaxanthin (0.03–2.15 mg/100 g); α‐tocopherol (0.69–6.39 mg/100 g); γ‐tocopherol (0.41 3.18 mg/100 g); C18:3n3 (25.4–70.3%); oxalic acid (70–630 mg/100 g); total phenolics (35.10 mg GAE/g extract); flavonoids (16.31 mg CE/g extract; 241 mg/g) | Vardavas et al. 2006a, b; Barros et al. 2011b; Martins et al. 2011; Morales et al. 2012a; Sanchez‐Mata et al. 2012 |
| Capsella bursa‐pastoris (L.) Medik. | Leaves | – | Nitrate (256 mg/100 g) | Bianco et al. 1998 |
| Chenopodium album L. | Leaves | 6.38 | Oxalic acid content (361–2027 mg/100 g) | Guil‐Guerrero et al. 1997a; Guil‐Guerrero and Torija‐isasa 1997; Bianco et al. 1998 |
| Chondrilla juncea L. | Leaves | 4.10–13.4 | C18:3n3 (56.3%); total phenolics (37.66 mg GAE/g); total flavonoids (7.43 mg CE/g extract) | Morales et al. 2012b; 2014; García Herrera et al. 2014b |
| Cichorium intybus L. | Leaves | – | Lutein (3.05–4.54 mg/100 g); neoxanthin (1.44 mg/100 g); violaxanthin (1.70 mg/100 g); α‐tocopherol (0.88–1.10 mg/100 g); γ‐tocopherol (0.58–1.97 mg/100 g); nitrate (12.9 mg/100 g); total phenolics (73.68 mg GAE/g extract; 122 mg/g; 306 mg cholorogenic acid/g); phenolic acids (15.8 mg caffeic acid/g); flavonoids (20.8 mg chlorogenic acid/g; 31.3 mg CE/g; 106 mg QE/g) | Salvatore et al. 2005; Conforti et al. 2009; 2011; Vardavas et al. 2006b; Morales et al. 2014 |
| Crithmum maritimum L. | Leaves | 4.68 | Carotenoids (3.30–5.60 mg β‐carotene/100 g); C18:1n9 (16.11%); total phenolics (1260 mg/g); flavonoids (35.6 mg QE/g); tanins (193 mg/g); nitrate (63 mg/100 g) | Guil‐Guerrero et al. 1996ab; 1997a; Males et al. 2003 |
| Daucus carota L. | Leaves | – | β‐carotene (1.77 mg/100 g); lutein (3.50 mg/100 g); α‐tocopherol (0.53 mg/100 g); C18:2n6 (60.9 %) | Vardavas et al. 2006a, b |
| Eruca vesicaria (L.) Cav. | Leaves | – | β‐carotene (1.15–1.40 mg/100 g); lutein (2.48 mg/100 g); α‐tocopherol (3.07); total phenolics (211 mg GA/g) | Bianco et al. 1998; Vardavas et al. 2006b |
| Fragaria vesca L. | Roots and vegetative parts | – | SFA (C16:0, 16.00%); C18: 3n3 (24.8%) | Dias et al. 2015 |
| Foeniculum vulgare Mill. | Leaves | 2.70–6.20 | β‐carotene (1.19 mg/100 g); lutein (3.66 mg/100 g); α‐tocopherol (1.66 mg/100 g); total phenolics (42.16 mg GA/g extract; 195 mg chlorogenic acid/g); hydroxycinnamic acids (495 mg chlorogenic acid/g); flavonoids (9.72 mg CE/g extract; 27.5 mg chlorogenic acid/g; 82.5 mg/g); nitrate (24 mg/100 g) | Trichopoulou et al. 2000; Zeguichi et al. 2003; Vardavas et al. 2006b; conforti et al. 2009; 2011; Morales et al. 2012a; Sánchez‐Mata et al. 2012; García Herrera et al. 2014; Vanzani et al. 2011 |
| Humulus lupulus L. | Young shoots | 4.85 | β‐carotene (0.49 mg/100 g); lutein (0.76 mg/100 g); neoxanthin (0.73 mg/100 g); violaxanthin (0.31 mg/100 g); α‐tocopherol (4.51 mg/100 g); γ‐tocopherol (8.98 mg/100 g; malic acid (295–1040 mg/100 g); total phenolics (55.83 mg GAE/g extract); flavonoids (9.56 mg CE/g extract) | Morales 2012; Morales et al. 2012a; García Herrera et al. 2013 |
| Malva sylvestris L. | Leaves | 4.76 | α‐tocopherol (20.1 mg/100 g); γ ‐tocopherol (4.80 mg/100 g); total phenolics (1692 mg GA/100 g); flavonoids (925 mg CE/100 g); nitrate (87.6 mg/100 g) | Franke & Hensbook 1981; Guil et al. 1997a, b; 1999a; Barros et al. 2010a; Romojaro et al. 2013 Hiçsomenez et al. 2009 |
| Montia fontana L. | Young leaves and stems | 4.44 | α‐tocopherol (2.90–6.08 mg/100 g); C18:3n3 (47.4–56.4%); total phenolics (75.53 mg GAE/g extract); flavonoids (16.67 mg CE/g extract) | Pereira et al., 2011; Tardio et al. 2011; Morales et al. 2012a, b |
| Papaver rhoeas L. | Leaves | 2.50–11.10 | Oxalic acid (124–850 mg/100 g); total phenolic (25.86 mg GAE/g extract; 239 mg chlorogenic acid/g); flavonoids (12 mg CE/g extract; 31 mg/g; 143 mg chlorogenic acid/g); nitrates (219–307 mg/100 g) | Trichopulou et al. 2000; Zeghichi et al. 2003; Conforti et al. 2011; Vardavas et al. 2006a; Sánchez‐Mata et al. 2012; García Herrera 2014; Morales et al. 2014 |
| Plantago lanceolata L. | Leaves | 3.71 | Phenolic acids (631 mg/g; 327 mg GA/g); hydroxycinnamic acids (509 mg chlorogenic acid/g); flavonoids (49.6 mg CE/g) | Guil‐Guerrero et al. 2001; Galvez et al., 2005; Gatto et al. 2011; Vanzani et al., 2011 |
| Plantago major L. | Leaves | 3.19–4.57 | Nitrates (94–108 mg/100 g) | Guil‐Guerrero et al. 1997a; 2001 |
| Portulaca oleracea L. | Leaves | – | Lutein (5.40 mg/100 g); zeaxanthin (0.2 mg/100 g); oxalic acid (681 mg/100 g) | Guil‐Guerrero et al. 1997a; Bianco et al. 1998; Dias et al. 2009 |
| Prasium majus L. | Leaves | – | Lutein (4.13 mg/100 g); β‐carotene (2.17 mg/100 g) | Vardavas et al. 2006a |
| Rumex obtusifolius L. | Leaves | – | Lutein (3.44 mg/100 g); β‐carotene (1.44 mg/100 g); α‐tocopherol (0.85 mg/100 g) | Vardavas et al. 2006a |
| Rumex papillaris Boiss. & Reut. | Leaves | 4.40 | C18:3n3 (51.8%); oxalic acid (3 –560 mg/100 g); total phenolics (104 mg GAE/g extract); flavonoids (39.5 mg CE/g) | Morales et al. 2012b; 2014; Sánchez‐Mata et al. 2012; García Herrera 2014 |
| Rumex pulcher L. | Basal leaves | 5.45 | Oxalic acid (57.7–730 mg/100 g); total phenolics (73.4 mg GAE/g extract); flavonoids (26.1 mg CE/g extract) | Morales et al. 2014; 2015; Sánchez‐Mata et al. 2012; García Herrera 2014 |
| Scolymus hispanicus L. | Peeled basal leaves | 7.00 | β‐carotene (0.1 mg/100 g); lutein (0.33 mg/100 g); total phenolics (21.51 mg GAE/g extract); flavonoids (8.38 mg CE/g extract) | Vardavas et al. 2006; Morales et al. 2014; García Herrera et al. 2014b |
| Silene vulgaris (Moench.) Garcke | Leaves | 2.60–6.63 | β‐carotene (1.029 mg/100 g); lutein (2.012 mg/100 g); α‐tocopherol (0.35–1.65 mg/100 g); total phenolics (26.72 mg GAE/g extract; 68.7 mg chlorogenic acid/g; 88.6 mg /g); hydroxycinnamic acids (230 mg chlorogenic acid/g); flavonoids (21.6 mg CE/g extract); nitrate (178 mg/100 g) | Zeguichi et al. 2003; Alarcón et al. 2006; Vardavas et al. 2006; Vanzani et al. 2011; Conforti et al. 2011; Morales et al. 2012; Egea‐Gilabert et al. 2013; García Herrera 2014 |
| Silybum marianum (L.) Gaertner | Peeled basal leaves | – | Oxalic acid (171–1889 mg/100 g); total phenolics (3.72 mg GAE/g extract); flavonoids (1.13 mg CE/g extract); nitrate (113 mg/100 g) | Bianco et al., 1998; Morales et al., 2012; Sánchez‐Mataet al. 2012 |
| Smilax aspera L. | Basal leaves and stems | 18.8 | α‐tocopherol (29.1 mg/100 g); β‐tocopherol (4.5 mg/100 g) | Demo et al. 1998; Cabiddu & Decandia 2000 |
| Sonchus asper (L.) Hill | Leaves | – | Total phenolics (102 mg chlorogenic acid/g; 308 mg/g); nitrate (72.6 mg/100 g) | Bianco et al. 1998; Gatto et al. 2011; Conforti et al. 2011 |
| Sonchus oleraceus L. | Young shoots | 2.60–5.57 | β‐carotene (1.05 mg/100 g); lutein (1.83 mg/100 g); α‐tocopherol (0.29–1.75 mg/100 g); oxalic acid (98–840 mg/100 g); total phenolics (51.33 mg GAE/ extract g; 217 mg chlorogenic acid/g; 220 mg/g); flavonoids (14.83 mg CE/g extract; 34.3 mg/g; 90.6 mg chlorogenic acid/g); nitrate (51.1–191 mg/100 g) | Guil‐Guerrero et al. 1998a; Trichopoulou et al. 2000; Zeghichi et al. 2003; Vardavas et al. 2006a,b; Conforti et al. 2009; Gatto et al. 2011; Vanzani et al. 2011; García Herrera et al. 2014b; Morales et al. 2014 |
| Tamus communis L. | Leaves | 3.50–9 | β‐carotene (0.44 mg/100 g); lutein (1.14 mg/100 g); neoxanthin (1.19 mg/100 g); violanxanthin (0;.62 mg/100 g); α‐tocopherol (0.12–3 mg/100 g); γ‐tocopherol (1.28–2 mg/100 g); C18:3n6 (42%); total phenolics (49.5 mg GAE/g extract; 220 mg/g); flavonoids (9.33 mg CE/g extract; 201 mg /g) | Barros et al. 2011b; Martins et al. 2011, Morales 2012; Morales et al. 2012a, b; Sánchez‐Mata et al. 2012; Pereira et al. 2013; García Herrera et al. 2013; García Herrera 2014 |
| Taraxacum officinale Weber/sect. Ruderalia | Leaves | – | Carotenoids (3.59 mg/100 g); α‐tocopherol (3.52 mg/100 g); C18:2n6 (62%); oxalic acid (986–1003 mg/100 g); nitrate (29.6 mg/100 g); %); total flavonoids (9.69 mg/g extract extract); total phenolic acids (43.24 mg extract/g extract); total phenolic compounds (52.93 mg/g extract) | Aliotta & Pollio 1981; Bockholt & Schnittke 1996; Bianco et al. 1998; Ayan et al. 2006; Gjorgieva et al. 2010; Gatto et al. 2011; Dias et al. 2014 |
| T. obovatum (Willd.) DC. | Leaves | 7.01 | Total phenolics (58.23 mg GAE/g extract); flavonoids (30 mg CE/g extract) | García Herrera et al. 2014b; Morales et al. 2014 |
| Urtica dioica L. | Leaves | – | β‐carotene (1.18–10.9 mg/100 g); lutein (5.25–5.97 mg/100 g); neoxanthin (0.43 mg/100 g); violaxanthin (1.92 mg/100 g); α‐tocopherol (14.4 mg/100 g); nitrate (92 mg/100 g) | Kudritsata & Zagorodskaya 1987; Wetherilt 1992; Bianco et al. 1998; Guil‐Guerrero et al. 2003 |
* CE, catechin equivalent; GAE, gallic acid equivalent; PUFA, polyunsaturated fatty acid; QE, quercitin equivalent; SFA, saturated fatty acid.
Table 7.7 presents data on levels of vitamins and minerals in wild leafy vegetables traditionally consumed in Europe obtained from scientific literature. Only data on species with significant nutrient contents have been recorded: 100 g of fresh material providing more than 15% of the generally accepted daily recommendations (FAO/WHO 2004; Trumbo et al. 2002).
In general, Chondrilla juncea L. stands out as a K, Fe, Cu, and Mn contributor; Portulaca oleracea for its Mg, Fe, Cu, and Mn content and also, although with higher variability, the leaves of some Urtica species (Mg and Fe levels). Wild edible plant foods are often good sources of calcium, as many wild leafy vegetables contain even higher levels than many foods widely accepted as good calcium sources, such as dairy products. Urtica dioica, Foeniculum vulgare Mill., Chenopodium album, Borago oficinalis L., and Eruca vesicaria L. Cav., among others, are considered as valuable Ca contributors, with values up to 300 mg/100 g fw, Urtica dioica being one of the richest Ca sources (246–982 mg/100 g fw). Moreover, the potential bioavailability of this macroelement is high in wild vegetables such as F. vulgare, Malva sylvestris L., Capsella bursa‐pastoris L., Eruca vesicaria and some Plantago species, that stand out due to their oxalic acid levels, being potentially better absorbed than calcium from other plant sources. Some wild greens can contain unusually high potassium levels, such as Beta maritima L., Chondrilla juncea, Scolymus hispanicus L., and Chenopodium album, reaching levels of 1 g/100 g fw or more (see Table 7.7). Regarding microelements, iron deficiency in Europe is not as serious as in other countries, such as in Africa or Asia. However, some plant foods may moderately contribute to daily iron intake. In this respect, Urtica dioica, Capsella bursa‐pastoris Medik., Chondrilla juncea, Portulaca oleracea, and Taraxacum obovatum (Willd.) DC. edible parts may contain high Fe levels (see Table 7.7).
As previously mentioned, wild greens are a great source of vitamins, particularly vitamin C, B9, and K. In the last few years, some authors have studied the vitamin C content (as total vitamin C, ascorbic acid, and dehydroascorbic acids) in different wild vegetables traditionally consumed in the Mediterranean area (Sánchez‐Mata & Tardío 2016). It is noteworthy that many of them stand out for their high vitamin C levels, such as leaves of Portulaca oleracea (up to 109 mg/100 g fw), Eruca sativa Hill. (125 mg/100 g fw), Daucus carota L. (over 127 mg/100 g fw), Capsella bursa‐pastoris L. (169 mg/100 g fw), and Chenopodium album (131–171 mg/100 g fw). Another neglected vegetable with high vitamin C values is Urtica dioica (238–333 mg/100 g fw), which easily provides the total daily recommendation of vitamin C (see Table 7.7).
Leafy vegetables, and particularly wild greens, could be a good source of dietary folates, and an increase in their consumption would be a good strategy to avoid the consequences of vitamin B9 deficiency. Despite a decrease in the consumption of fruits and vegetables in Europe, there are no serious problems of folate deficiency, as its supplementation is recommended primarily in pregnant women (FAO/WHO 2004). The prevalence of neural tube defects varies across the EU, occurring in 0.4–2.0 cases per 1000 births; the range of variation is attributed to differences in reporting and collecting data in the different European countries (European Food Safety Authority 2008). To our knowledge, there are not many data available about folic acid and folate content in wild vegetables in general, and particularly in Europe. Considering published values, it could be stated that many of them have high folate values, particularly Rumex pulcher L. (478 µg/100 g fw), followed by Beta maritima, Anchusa azurea Mill., F. vulgare, Silene vulgaris (Moench) Garcke., Cichorium intybus L., and Asparagus acutifolius L. All these could be considered as a source of this nutrient, reaching almost 200 µg/100 g fw (Morales et al. 2015), thgus being able to provide the whole daily recommendation (200–400 µg/day) in a 100 g portion (Cuervo et al. 2009).
Regarding liposoluble vitamins, carotenoids are considered of great interest due to the provitamin A activity of some of them (α‐carotene, β‐carotene, and cryptoxanthin, mainly), but also for other bioactive properties such as antioxidant and antiinflammatory capacity (Elliott 2005; Stahl & Sies 2012). There are very few studies regarding carotenoid content in wild greens but some indicate interesting vitamin A values (expressed as estimated retinol activity equivalents (RAE)), with Urtica dioica followed by Cichorium intybus and Daucus carota the richest species (476, 245 and 238 µg/100 g, respectively) (see Table 7.7). However, in leafy vegetables, nonprovitamin A carotenoids, such as xanthophylls (lutein, neoxanthin, and violaxanthin), are usually the major carotenoids, even in many cases at higher levels than β‐carotene (García Herrera 2014; Guil Guerrero et al. 2003;Salvatore et al. 2005). Lutein is present in wild green vegetables, with Urtica dioica, Portulaca oleracea, Cichorium intybus, and Prasium majus L. beingsome of the richest species with lutein values of 4.13–5.97 mg/100 g fw (see Table 7.7).
Wild European vegetables, such as Smilax aspera L., Malva sylvestris L., Apium nodiflorum, and Montia fontana L., and tender shoots, such as A. acutifolius and Bryonia dioica, have high vitamin E content (2.62 and 29.1 mg/100 g in A. nodiflorum and S. aspera, respectively), calculated according to the FAO/WHO methods (2004); α‐tocopherol was the main isoform (4.5 and 29.1 mg/100 g in M. fontana and S. aspera, respectively) (see Table 7.8). In some cases γ‐tocopherol was also found in relatively important amounts in Humulus lupulus, Malva sylvestris, S. aspera, and B. dioica (8.98–3.18 mg/100 g).
Vitamin K, mainly as phylloquinone (K1) vitamer, is synthesized by green vegetables and is widely distributed throughout the diet. In general, relative values in green leafy vegetables are around 400–700 µg/100 g. Vitamin K deficiency is very uncommon in humans, aside from a small percentage of infants who suffer from hemorrhagic disease of the newborn, a potentially fatal disorder. In adult humans, a prolonged blood‐clotting time is the predominant, if not sole, clinical sign of vitamin K deficiency (FAO/WHO 2004). There are very few studies regarding vitamin K levels in wild vegetables. However, Vardavas et al. (2006) demonstrated that most of them provide the necessary amount to cover 100% of daily recommended intake (50–65 µg/day; FAO/WHO 2004) and can be considered as very good sources of this nutrient (more than 11.3 µg/100 g, according to European Regulation 1169/2011), as can be seen in Prasium majus, Rumex obtusifolius L., Daucus carota, and F. vulgare which contain the highest levels (more than 300 µg/100 g fw).
Other important bioactive compounds in wild edible European greens are dietary fiber, phenolics, organic acids, and polyunsaturated fatty acids (PUFAs), which are shown in Table 7.8. Several studies show that the ingestion of suitable quantities of dietary fiber provides many beneficial effects such as the regulation of intestinal function, improvement of glucose tolerance in diabetics, and prevention of chronic diseases such as colon cancer (Mongeau 2003; Pérez Jiménez et al. 2008). From the nutritional standpoint, fiber is the most important component of wild plants. The plant species with the highest fiber contents include Beta maritima, Tamus communis L., Scolymus hispanicus L., and Taraxacum obovatum with values up to 7 g/100 g, with Smilax aspera and Chondrilla juncea the ones with the highest values (18.8 and 13.4 g/100 g, respectively). In most cases wild European edible greens (see Table 7.8) could be considered as source of dietary fiber (more than 3 g/100 g fw).
Phenolic compounds, as secondary plant metabolites, are gaining greater prominence as bioactive agents; total phenols and flavonoids have an important role in antioxidant defense mechanisms in the plant, and there are a great number of in vitro and in vivo studies, using animal and human cell cultures, suggesting that these bioactive compounds of wild plants show a positive effect on human health, such as antioxidant, antitumoral, antimutagenic, antimicrobial, antiinflammatory, and neuroprotective properties (Carocho & Ferrerira 2013). There are several studies on the phenolic composition of wild edible plants, identifying phenolic acids (in some cases different hydroxycinnamic acids) and flavonoids such as proanthocyanidins and anthocyanins. These compounds have been reported in wild species traditionally consumed in Europe, mainly focused in the Mediterranean area (Conforti et al. 2008, 2011; García Herrera et al. 2014a; Martins et al. 2011; Morales 2011; Morales et al. 2012a,b, 2014; Pereira et al. 2011; Salvatore et al. 2005; Vardavas et al. 2006; Zeghichi et al. 2003, among others). Polyphenols can be measured (e.g. spectrophotometry, HPLC‐DAD, HPLC‐MS) and expressed differently (e.g. as gallic acids, cathechin, chlorogenic acid, quercetin equivalents or as a sum of different individual compounds), therefore in some cases it is very difficult to compare results. European wild species such as Eruca vesicaria (L.) Cav., Montia fontana, and Plantago lanceolata L. stand out due to their total phenolic content (211, 277 and 327 mg gallic acid equivalent (GAE)/g methanolic extract, respectively), while Apium nodiflorum, P. lanceolata, M. fontana, and Anchusa azurea were reported to have high flavonoid contents (45.5, 49.6, 52.3 and 84.8 mg catechin equivalents (CE)/g, respectively). Regarding other polyphenol families, tannin content was reported in Crithmum maritimum L. (193 mg/100 g fw) and hydroxycinnamic acids in P. lanceolata, F. vulgare, and S. vulgaris (230, 495 and 509 mg chlorogenic acid/100 g fw, respectively).
Polyunsaturated fatty acids (PUFA) play an important role in human nutrition, being associated with several health benefits. Unsaturated fatty acids are associated with a reduced risk of developing cardiovascular disease, inflammatory and autoimmune diseases such as asthma, Crohn’s disease and arthritis, and certain cancers, including colon, breast, and prostate (Simopoulus 2004). Vegetables are rich in PUFA of n‐3, n‐6, and n‐9 series, such as α‐linolenic, linoleic, and oleic acids, respectively. Wild edible plants contain in general a good balance of n‐6 and n‐3 fatty acids, particularly Anchusa azurea, Bryonia dioica, Chondrilla juncea, Montia fontana, Rumex papillaris, and Tamus communis due to their high n‐3 fatty acid proportion (see Table 7.8), mainly as α‐linoleic acid (ALA; C18:3n3).
In Europe, wild species are traditionally gathered due to their great versatility in handling and consumption, and may have great potential as a source of functional compounds. This justifies the need to preserve their traditional uses, as an alternative to the variety of currently available cultivated vegetables or as ingredients of new dietary supplements and/or functional foods.
Despite all the information about the nutritional benefits of wild edible plants, when studying the health implications of their consumption, the possibility of negative effects should also be considered. From ancient times, empirical knowledge about wild plant properties has governed their utilization all over the world. Observation of what animals or other humans ate suggested which plants were edible and which may be hazardous, and this information was transmitted through generations. The presence of these wild vegetables in the human diet provided fiber, vitamins, minerals, and other bioactive compounds necessary to avoid many deficiency diseases and allowed hunter‐gatherers to achieve generally a good health status; in fact, some of the features of Paleolithic nutrition have evolved negatively in modern diets (Simopoulos 2004).
Many wild plants were also used as natural remedies to cure diseases, sometimes with success, other times failing; in some cases the cure was achieved spontaneously and the medicinal property was erroneously attributed to the plant used. Other wild plants were also known as natural poisons, and so warnings were transmitted about their erroneous use. In other cases, they may be intentionally used: impregnated in arrows and darts for hunting or fighting (e.g. curare’s paralyzing principles or Strychnos spp. extracts); for Greek or Roman executions (e.g. Socrates, condemned by the senate of Athens to drink an extract made of Conium maculatum L., the poison hemlock, in 399 BC); or even for murder (e.g. using aconitum root) (Diggle 2003; Oghno 1998; Philippe & Angenot 2005). In this context, food, medicine, and poison are three concepts that may sometimes be very close in nature, as stated by Hippocrates in the fifth century BC (“let food be your medicine and medicine be your food”) and Paracelsus in the sixteenth century AD (“dosis sola facit venenum” ‐ the dose makes the poison).
Later, acquired empirical knowledge was subjected to investigation, first by alchemists or apothecaries and later by naturalists, botanists, doctors, and pharmacists. As laboratory techniques developed, the mechanisms of action and the structure‐activity relationships of chemical compounds were studied. In some cases, a true biological activity was not found, but in other cases, the empirically claimed properties were confirmed. Thus many traditional plants continued to be used but under the control of health professionals and authorities, and in some cases this has lead to the industrial development of medicines made with different plant parts (e.g. Plantago seeds as laxatives) or isolated active principles, either native (e.g. digoxin from Digitalis species or cocaine from Erythroxylum coca Lam. leaves) or chemically modified (e.g. acetylsalicylic acid derived from salicin obtained from Salix alba L. bark or antiasthmatic substances semisynthesized from atropine extracted from Atropa belladonna L.) (Bahar et al. 2008; Evans 2009).
Unfortunately, with the intense development of agriculture in the 20th century, many of the traditional practices of gathering wild plants from nature, for either food or medicinal use, have almost disappeared, displaced by cultivated crops. Demographic movement from fields to cities has also meant that a great part of the knowledge achieved by humans through centuries has been forgotten in just two or three generations. Nowadays, new trends of recovering these practices are arising, as a new philosophy of life based on returning to nature, in developed societies, or as a tool to fight against food shortages, in developing ones.
The revalorization of traditional wild plant use is positive and valuable; however, when the knowledge chain has been interrupted for several generations, caution should be exercised. Many people are keen to return to natural ways of life and try to imitate their ancestors by collecting plants and fungi, with the wrong idea that all “natural” products are harmless. Those who gathered wild plant foods from nature in the past had been familiar with these practices since their childhood, watching their parents or grandparents and learning about edibility of species and the proper way they should be handled. The experience of generations honed their knowledge, but some people today feel that they can do the same with very scanty information (“A friend told me…,” “I saw it on the internet…,”,“This is similar to a picture I saw…”), and this may lead to mistakes, sometimes with bad consequences.
Apart from the presence of naturally occurring compounds, wild plants can carry contaminants, either chemical pollutants accumulated from the soil (when they grow near mines or highly industrialized areas) or parasites such as Fasciola hepatica (typically living on watercress) (Couplan 2002; Fawzi et al. 2003). The latter may be eliminated by washing the plant with diluted vinegar or by cooking, a practice often performed by the population that used to gather watercress but not always known by many “novel gatherers.”
Regarding the naturally occurring compounds, in the latest reports (1989–2006) from different European and American official institutions on toxicology and toxicovigilance, about 2.5–5% of reported poisoning cases are due to plants, of which 80–90% were children accidentally ingesting toxic plants (specially infants under four years old swallowing fruits with attractive bright colors), and 10–20% were adults. Of adult poisonings, the main causes were intentional suicide, hallucinogen purposes, or errors in identification or utilization (Flesch 2005; Fourasté 2000; Moro et al. 2009). Deep knowledge of botany or long experience in plant gathering is necessary to safely collect wild plants, since identification mistakes often occur between similar species (see some examples in Table 7.9), which can lead to serious poisoning. One cause of these misidentifications may be the fact that the presence of flowers often differentiates edible species from toxic ones, and since the optimal time for gathering leafy vegetables is when leaves are young, before flowering, confusion could easily occur (Bergerault 2010).
Table 7.9 Some examples of confusions between edible vegetables and toxic wild plants (Bergerault 2010).
| Edible species (edible parts) | Resembling species (toxic principles) |
| Gentiana lutea L. (subterranean parts) | Veratrum album L. (alkaloids: protoveratrins, jervin) |
| Brassica napus L. (root) | Aconitum napellus L. (alkaloids: aconitin) |
| Symphytum officinale L. (leaves) | Digitalis purpurea L. (cardiotonic heterosides: digitoxin, gitoxin, digitalin) |
| Laurus nobilis L. (leaves) | Nerium oleander L. (cardiotonic heterosides) Prunus laurocerasus L. (cyanogen glucosides) Daphne laureola L. (diterpens) |
| Chenopodium bonus‐henricus L. (leaves, inflorescences) | Arum maculatum L., A. italicum L. (cyanogenetic glucosides) |
| Leucanthemum vulgare Lam. (young leaves) | Senecio jacobaea L. (alkaloids: senecionin) |
| Sisymbrium officinale (L.) Scop. (leaves) | Erysimum cheiranthoides L. (cardiotonic heterosides) |
| Stellaria media (L.) Vill. (leaves, young stems) | Anagallis arvensis L. (hemolytic saponins: cyclamin, cucurbitacins) |
| Allium ursinum L. (leaves) | Colchicum autumnale L. (alkaloids: colchicin) |
| Abies alba Mill. (tender young shoots) | Taxus baccata L. (pseudoalkaloids: taxoids) |
In other cases, toxicity is linked to eating the wrong part of the plant (e.g. stems of rhubarb are edible, while leaves are rich in oxalic acid and subterranean parts contain antraquinons with purgant effects). Toxic substances may also depend on the maturation stage of the plant (especially in some fruits, where often alkaloid levels are much higher in immature fruits than in mature ones, e.g. Sambucus nigra L. or Solanum nigrum L.). In some cases, toxins may be eliminated with the proper treatment; for example, oxalic acid in some Rumex species may be harmful at the levels detected in the raw product, but can be mostly removed by cooking; aconite alkaloids are extremely toxic, but notification of accidental intoxications with Aconitum napellus L. is scarce since they are heat labile (Bergerault 2010; Evans 2009; Morales 2012).
Some naturally occurring compounds in plant tissues showing certain degrees of toxicity are (Bruneton 2005; Cameán & Repetto 2006; Evans 2009).
Special attention should be given to the Solanaceae family, which has members known for containing tropan alkaloids (Atropa belladonna L., Hyoscyamus niger L., Datura stramonium L.) or glycoalkaloids (based on a steroid structure bonded to different sugars). Tropan alkaloids may cause serious intoxications, for example by smoking their leaves or accidentally confusing their fruits with other edible berries such as Vaccinium myrtillus L. (frequently in children) (Nogué et al. 2009). Solanine and chaconine are the major glycoalkaloids in potatoes (Solanum tuberosum L.), being highly toxic by inhibiting acetylcholinesterase. Formal guidelines limit the total glycoalkaloid concentration in commercial potatoes to 200 mg/kg fw as a safe value (Friedman et al. 2003), taking into account that around 140 mg/kg a bitter taste is usually detected (Deshpande 2002). Other Solanaceae species have different alkaloids, such as tomatidine derivatives in tomatoes (Solanum lycopersicum L.) or solasodine derivatives found in eggplants, at low levels in cultivated species such as Solanum melongena L., but in higher levels in some of their wild relatives such as Solanum macrocarpon L. or Solanum aethiopicum L. (Sánchez‐Mata et al. 2010). The fruits and leaves of these species are widely eaten in Africa.
However, the border between what is edible or not is not always so clear. For example, S. nigrum is reported to be eaten in Africa (Odhav et al. 2007; Steyn et al. 2001), while this species has been reported to be toxic due to high levels of glycoalkaloids (FAO 1988; Mohy‐ud‐dint et al. 2010). Taxonomic questions may be involved in this discrepancy: the FAO (1988) states that frequently the edible S. americanum Mill. is erroneously identified as S. nigrum while Mohy‐ud‐dint et al. (2010) postulate that S. nigrum complex includes S. americanum and S. nigrum. Therefore, an in‐depth chemotaxonomic study of the literature about these plants should be undertaken. Also, genetic or environmental factors can influence alkaloid content, giving rise to a wide variability in the chemical composition of plants of the same species. This occurs in many crops, where sweet and bitter varieties can be differentiated among the same species. Another example is the fruits and roots of the Cucurbitaceae family, which may also contain cucurbitacins, which have lead to some cases of intoxication with bitter zucchini fruits in America and Australia. Momordica spp., whose fruits and leaves are appreciated for food consumption in Africa and Asia, may also have either bitter or nonbitter fruits with the presence of momordicosides (Gry et al. 2006).
The Apiaceae family is also important from the point of view of the correct identification of its members. Several species of this family are widely eaten throughout the world: Daucus carota L. (root, fruits), Angelica sylvestris L. (stems, fruits), Apium graveolens L. (leaves, young stems), Petroselinum spp. (leaves, young stems), Foeniculum vulgare Mill. (leaves, young stems, fruits), Pimpinella anisum L. (fruits), Pastinaca sativa L. (leaves), and Chaerophyllum aromaticum L. (leaves). However, some of these vegetables may resemble other extremely toxic species, such as Conium maculatum, Aethusa cynapium L. (containing the lethal piperidine alkaloids coniine and conicein, respectively), Cicuta virosa L. or Oenanthe crocata L. (containing the very toxic polyacetylenes conicein and oenanthotoxin, respectively); they have been responsible for several deaths in recent decades, caused by erroneous identification of these species (Bruneton 2005).
Other potentially toxic compounds are not a problem for most people in the amounts found in edible plants, but may be particularly harmful for particular individuals, such as oxalates being both an antinutrient (forming a nonabsorbable Ca complex) but also provoking renal calculus, a concern for people suffering from renal disorders; the β‐glucosides, vicin and convicin, causing favism in people with a genetic deficiency of glucose‐6‐phosphate‐dehydrogenase; or nitrates causing metahemoglobinemia in infants. Many of these substances may also occur cultivated vegetables, acting as oxalate or nitrate accumulators, such as spinach or beet (Spinacia sp., Beta sp.) leaves.
Risks related to wild plant consumption may also arise because of the wrong use of some plant species, sold without control by health authorities or wrongly used in food supplements, or even medicines. For this reason, in many countries, health authorities are making efforts to regulate the use of plants in commercial preparations to promote consumer safety. For example, in 2009 the European Food Safety Authority (EFSA) published a compendium of botanicals that require specific attention while assessing the safety of products containing those species, due to previous reports confirming toxic, addictive, psychotropic or other substances of concern (European Food Safety Authority 2009). This publication is aimed to guide their use in food supplements, and requires correct interpretation. It should not to be considered as a list of toxic plants; in fact, it includes many species widely used as food all over the world, such as lemons (Citrus limon (L.) Burm. f) and peaches (Prunus persica (L.) Batsch). This does not mean that they are toxic as eaten, but that some substance of concern may have been described in some parts of the plant, being harmful in small or large quantities. These quantities may sometimes significantly exceed what an adult can eat, but could easily be reached if an extract of the plant is included as an ingredient in a food supplement or pharmaceutical preparation. A good example would be nutmeg (Myristica fragrans Houtt.), widely used in gastronomy as a spice for its pleasant flavor; however, high doses of nutmeg or its extract (containing miristicin, elemicin, and safrol) are toxic for humans.
Advances in communication technology may sometimes contribute to sending the wrong messages to the population; nowadays, people receive high levels information without having a clear idea of what is reliable or not. So, besides health authority surveillance and recommendations, to avoid health problems derived from the incorrect use of wild plants, some popular myths should be discarded. People should understand that “natural” is not a synonym for “safe” and that the recovery of lost knowledge about wild edible plants is not an easy task when the knowledge chain has been broken for generations.
Being conscious of these concerns, the lost knowledge could be safely recovered through several strategies:
Taking into account the warnings regarding misidentification of species or improper use, the revalorization of these traditional foods should be encouraged, as they represent valuable sources of nutrients, often lacking in many societies, and also contribute to diet diversification and preservation of the traditional knowledge, food habits, and identity of each geographical area.
Some species are widely spread and consumed as leafy vegetables in many different parts of the world, such as purslane (Portulaca oleracea), fat hen (Chenopodium album), nettles (Urtica dioica, U. urens), watercress (Nasturtium officinale), and spinach (Spinacia oleracea). Also the leaves of Rumex spp., Sonchus spp., Mentha spp., and Brassica spp., with differences in the species growing in each environment, are traditionally eaten in most places and cultures. Some other wild vegetables such as Amaranthus spp., Centella asiatica or different species of Cucurbita, often eaten in tropical Africa, America and Asia, are also widely used species.
These vegetables, among other species characteristic of specific geographical areas, are a valuable tool to improve the health status of populations by providing fiber, vitamins (folate, vitamin C, provitamin A), and minerals (K, Ca Fe, Mn in some cases), as well as other bioactive compounds such as antioxidants, for the human diet, in both developed or developing countries. Food‐based strategies devoted to revalorizing these vegetables, driven by nongovernmental organizations and other local institutions, should be encouraged, including promoting gathering of autochthonous plants from the wild; acquisition of skills for their cultivation in home gardens (both at a very minimal cost), or improving bioavailability of nutrients by home preservation and preparation of food. Nutrition education should always be a complementary activity to ensure the effectiveness of these food‐based approaches.