Getting Started |
Background
The earliest evidence for land plants comes from the Ordovician period around 460 million years ago (460 Ma) where spores produced by plants resembling present day mosses and liverworts have been found. The evolution of stronger stems, water transporting tissues, and seeds, enabled plants to diversify and exploit new niches. By the Carboniferous period (358–298 Ma) tropical forests, dominated by tree-like species and primitive seed-bearing plants, formed vast ‘coal-forming’ forests in the northern hemisphere. Ancestors of plants that we are familiar with today such as conifers (pines, firs, spruces, monkey puzzles) appeared later in the Carboniferous period (315 Ma). The significant coal deposits of South Africa, eastern Australia, India and South America are much younger, formed from deciduous forests that covered temperate southern regions as far south as 80 degrees latitude. The most spectacular change to global vegetation occurred in the Cretaceous period when flowering plants rose to ecological dominance (100 Ma) replacing a vegetation dominated by conifers, ferns and groups of seed plants now extinct. Today just five lineages of seed plants survive, the most diverse group being the Flowering Plants with about 300 000 species. The long geological history and diversity of land plants contrasts markedly with that of the genus Homo, to which we belong. Evidence of early humans appears just 2.1 million years ago, and modern humans (Homo sapiens) have been here for only 300 000 years.
The term botany is derived from a Greek word meaning ‘plant’ and is the branch of science that investigates plants. However, plants were important to the economy of humankind long before any scientific studies took place. People had to know which were good to eat, which were harmful, had medicinal value or could be used for making shelters, baskets and clothing. Some of the earliest non-religious books were the herbals which contained descriptions of plants with their medicinal properties and recipes for herbal remedies. Plants containing hallucinogenic compounds are part of the folklore in many lands, having a particular place in religious ceremonies. One important ingredient of the witches’ brews of mediaeval Europe was Deadly Nightshade, a relative of the potato and tomato. The use of Cannabis is well-documented; in Egypt, for example, it has been in use for over 4000 years.
Systematics and taxonomy are two interlinked branches of modern botany, and deal with plant form, how plants resemble each other or how they differ, how they can be assembled into groups that reflect their evolutionary history, and how these different forms and groups can be uniquely described and named. But why are names so important? It is certainly easier to talk about a plant, or buy one for the garden, if you know what it is called. All plants have a scientific name that applies to one sort of plant only and has international recognition. These names are the keys to the wealth of information about plants available in the scientific literature and increasingly via the internet. Many amateur naturalists shy away from using them but they are useful in recognising relationships as well as being necessary for accurate identification, which is an essential prerequisite to any discipline that involves plants.
Some essential information
In order to identify any Flowering Plant, in a scientific and conclusive way, one needs to understand:
• the structure of the flower, and of the vegetative parts
• the botanical terms used in descriptions
• how to use reference books, and in particular, botanical keys
• something about plant relationships (the classification system).
These topics are discussed more fully in Chapters 2 to 7; the following paragraphs introduce a few terms and concepts that form necessary background.
The system of naming plants now in use was established in 1753 by a Swedish naturalist Carolus Linnaeus. When Linnaeus put forward his scheme in the book Species Plantarum, all organisms were classified into one of two kingdoms: plants or animals. The criteria for their separation were that plants were immobile and neither ate nor breathed, whereas animals moved, breathed and ate. As new organisms were discovered they were assigned to one of these two kingdoms, but by the early twentieth century it had become obvious that this traditional division could not be sustained. For introductory purposes here, a simplified division of the plant kingdom can be made into Algae (including seaweeds and freshwater forms), Mosses and other moss-like plants, Ferns and their allies, Conifers (pines, cypresses, firs and their relations) and Flowering Plants. The Fungi, including moulds, mushrooms and toadstools, are no longer considered part of the plant kingdom.
Many flowers are large, brightly coloured and scented, while others may be quite inconspicuous, but the plants that bear them all make up the group ‘Flowering Plants’. Technical names proposed for this group include Angiospermae, Magnoliophyta, and Anthophyta. Traditionally, two major subgroups of Flowering Plants have been recognised, commonly known as the Dicotyledons and Monocotyledons. (These names are often contracted to Dicots and Monocots and that usage will be adopted in this book.) Continuing research over the last several decades, particularly using the advances in techniques for extracting and comparing plant DNA samples, has necessitated a reassessment of these traditional major groups.
The main subgroups of Flowering Plants are further divided into orders, families, genera (singular—genus) and species. A species is a kind of plant, possessing a unique set of characteristics; similar species are grouped into genera. A species has a two-word Latin name, e.g. Acacia pycnantha; the first word is the name of the genus (Acacia) and the second is the specific epithet (pycnantha). The common name of this plant is Golden Wattle. Classification and nomenclature are dealt with more fully in Chapter 6.
In contrast to scientific names, common names are not subject to any rules or guidelines of construction or use. Many plants have one or more common names in the language of the region where they grow, but conversely many plants have no common name at all. Further, common names are not universal (the same name may be used for different plants in different regions), so their use may lead to errors and confusion. The use of scientific names is recommended as they eliminate many mistakes in identity and are international in application.
In previous editions of this book common names have been written with lowercase initial letters. This convention however can make the limits of the name unclear, for example which of the words ‘common red-flowered yellow gum’ are simply qualifying adjectives and which should be read as part of the name? In this edition we have changed to uppercase initial letters for common names where these refer to particular species or groups. In more general contexts, lowercase may be used. As well, we have avoided hyphens within common names unless the inclusion of a hyphen significantly enhances clarity or readability.
Much of this book is taken up with description and illustration of flowers. Why is there such emphasis on floral structure? Linnaeus based his system of classification on the characteristics of the sexual reproductive organs and these are found in the flower. Even today floral structure still plays a significant role in plant classification, despite much additional information being available, for example, about anatomical, chemical, and genetic characteristics. An understanding of the way flowers are constructed is a major key to identification because flowers are usually readily accessible, and the relative positions of the various floral parts (the floral structure) remains reliably constant, even if a species grows in a range of habitats which may result in considerable variation in the general appearance of the whole plant. Compared to, say, features of stems and leaves, the number, appearance and relative position of the floral parts are more readily described in a way that can distinguish one species from another. In addition, for people who wish to get to know plants, whether for professional or interest reasons, flowers are generally more memorable, and the details of their structure can assist with establishing a mental register of species and groups.
An appreciation of the way flowers are constructed, and familiarity with the descriptive language, will help the reader to see that plants are not isolated organisms, but form natural groups that are related to each other. Some groups are easy to spot: the orchids, wattles, gum trees and bottlebrushes, for example. However, the close relationships of genera in a family are not always immediately obvious, for example, the grouping of gum trees and tea-trees, or of proteas and grevilleas. We hope the use of this book will enable you to appreciate these relationships and increase your awareness of the amazing diversity and beauty of the world of Flowering Plants.
It is necessary to stress that this book does not present all there is to know about floral structure. It deals with the most common structural patterns and their variations, but some variations and exceptions are not included. The examples are drawn from plants common in gardens and the bush of south-eastern Australia, thus, many tropical families have not been mentioned. However, the principles of identification are not geographically confined and the basic information is applicable in any region. Having mastered the information presented here, the interested reader will have little trouble in working with plant identification manuals for other parts of the world.
Guidelines and conventions for pronunciation of botanical names can be found in Tasmanian plant names unravelled by Wapstra (et al., 2010), Plant names: A guide to botanical nomenclature by Spencer and coauthors (2007) and Western Australian plant names and their meanings by Sharr (1996). Actual practice varies, particularly from country to country. Sometimes it is the loudest voice that holds sway. The standard ending for family names (–aceae) is usually pronounced, in Australia, as ‘ay-see’. For example the Citrus Family Rutaceae = Ru-tay-see, and the Myrtle Family Myrtaceae = Mer-tay-see. Sometimes a slight extra emphasis is placed on the last syllable, effectively pronouncing both the ‘e’ and the ‘ae’. The standard ending for the names of orders (–ales) is usually pronounced ‘ay-lees’. Thus for the Citrus group, the order Sapindales = Sap-in-day-lees, and the order Myrtales which includes the Eucalypts = Mer-tay-lees.
Using this book
One way of finding out about floral structure and coming to grips with the terminology is to work through the book from the beginning, referring to living plants as often as possible. Throughout the text, important terms when first introduced appear in bold type. These terms are commonly encountered in books dealing with plant identification.
Another approach is to compare the labelled illustration or photograph of a fuchsia or a grevillea, for example, with flowers from the garden. It is usually not essential to have the exact plant illustrated; often a related species will be sufficiently similar. The illustrations are specifically intended as a visual aid to the type of flower structure commonly seen in the various families. In a number of cases, two or more species in a genus have been drawn, allowing an appreciation of the close similarity in structure at this level. (See Figs. 28–9, 48–50, 58–62, 84–8, 105–6.) Unfamiliar terms can be checked in the glossary, which will often refer to an illustrated example in the text. Many illustrations are included in order to show the application of terms in a wide range of examples.
Within the text, we have been selective when referring to figures and plates that illustrate a particular feature of plant structure. There may be more examples than the one(s) we have chosen.
In Chapter 8, families have been numbered in sequence purely for ease of navigation within this book. The numbers have no other relevance.
It must be remembered that, just like human beings, individual plants within a species often vary to some degree in their general appearance. Any attempt at neatly summarising the characteristics of a species (or genus or family) will almost certainly run the risk of overlooking unusual variations. Virtually all such comments relating to various plant groups possessing particular characteristics should be read as if preceded by the word ‘usually’.
The drawings in Chapter 8 were made from actual specimens, arranged to show as many relevant features as possible. To make comparisons easier, most flowers are drawn with the stalk at the bottom. This may not be how they would naturally appear on the plant and some mental adjustment may be necessary. The drawings are as accurate as possible, but some natural variation is likely—part of the experience of getting to know plants. Slight exaggeration has been necessary in a few cases to improve clarity, such as enlarging the gap between closely adjacent parts. Dashed lines usually indicate a part cut away to reveal the structure behind (e.g. Fig. 22b).
The transverse section (T.S.) of the ovary in each case has been drawn to illustrate the placentation. It may not be a true ‘section’, as some depth has occasionally been added to make parts more obvious.
In sections and half flowers (which are exact halves), the cut surfaces are unshaded, and the adjacent surfaces have usually been shaded to try to make this clear. Shading within the ovary represents the loculus or cavity that contains the ovules. Figure 21 shows the way in which the flowers were cut to give the views drawn in most of the illustrations.
Labelling has occasionally been omitted from parts of drawings and photographs that were difficult to pinpoint accurately or clearly. In some cases, a composite structure, for example, the ovary, is difficult to label with a single arrow. Reference to the diagrams in Chapter 2 should clarify this.
The captions for Figures 22–132 begin with the botanical name, in italics, of the species illustrated, followed by the common name (in parentheses) if one is available. Usually a floral formula is included which summarises the basic floral structure shown in the drawing. These formulae are explained at the end of Chapter 2. The short descriptions of the plant together with the illustration, should provide enough information to enable the species to be ‘identified’ for practice in working with keys. This procedure is explained in Chapter 7.
The magnification of each part of an illustration is included at the end of the caption. Measurements made on the drawings, when divided by the magnification, will give the real dimensions. This will sometimes be very small—the ovary in Leucopogon virgatus (Fig. 106), for example, is about half a millimetre across.
The captions for the plates follow a similar pattern except that magnifications have been omitted—measurements given in the description will give an idea of size. Floral formulae are not included if details of the flower are not visible.