Also known as phytology, or plant science, botany is the scientific study of plant life. Botany includes a wide range of related scientific disciplines that examine plant structure, growth, reproduction, and development, among other studies, in more than 550,000 plant species.
Early Studies in Botany
Human civilization depends on a knowledge of plants and their cultivation, making botany one of the oldest sciences. In many aspects, the study of botany dates to early tribal lore that was used to identify different types of plants as being poisonous, edible, or medicinal.
The taxonomy (classification) of plants—plant systematics—began in the fourth century B.C., with the publication of Historia Plantarum (On the History of Plants), by the Greek philosopher Theophrastus (ca. 371–286 B.C.), a pupil of Aristotle. Written around 300 B.C., this work did not propose a formal classification theme; instead, it used a combination of groupings from folklore and the observation of growth form. Together with the companion book, Causis Plantarum (On the Causes of Plants), Theophrastus’s work built on his teacher’s library and unpublished works, serving as an indispensable guide for the study and teaching of botany through the 17th century.
Another important early compendium was Materia Medica by Dioscorides, a first century A.D. Greek physician in the Roman army. This work, compiled around 65 A.D., contained more than 500 botanical descriptions and herbal remedies, and remained the single most important reference on medicinal plants for the next 16 centuries.
Modern Botany
In the early 16th century, Gaspard Bauhin (1560–1624), a Swiss botanist, began to develop a more modern classification system for plants. His Pinax Theatri Botanica (An Illustrated Exposition of Plants), published in 1623, described and classified some 6,000 plant species, using traditional groups such as trees, shrubs, and herbs. At around the same time, the Italian physician and botanist Andrea Cesalpino (1519–1603) began to classify plants according to their fruits and seeds. His De Plantis Libri XVI, published in 1583, helped establish classification by the organs of fructification as the foundation of the botanical system.
More detailed classification schemes were introduced during the 17th century by the English naturalist John Ray (1627–1705) and the French botanist Joseph Pitton de Tournefort (1656–1708). Ray established species as the basic unit of taxonomy and listed more than 18,000 plant species in his work Historia Plantarum, published in 1686. Tournefort was the first to clearly define the concept of genus for plants.
Botany as a science developed more rapidly in the 17th century, owing in part to the invention of the microscope, which enabled more detailed examination of plant life. In particular, the English scientist Robert Hooke (1635–1703) used an early microscope to discover cells in living plant tissue, as detailed in his work 1665 work Micrographia (Small Drawings).
During the 17th and 18th centuries an increased understanding of plant processes moved the field ahead dramatically. Belgian scientist Jan Baptista van Helmont (1580–1644) demonstrated that plant growth had little to do with soil and identified CO2, while the famed English chemist Joseph Priestley (1733–1804) showed that growing plants “restored” air from which the oxygen has been removed. And the Dutch physiologist Jan Ingenhousz (1730–1799) proved that light is required for plants to restore air. Combined, these and other studies formed the basis for modern plant physiology.
In the early 18th century, Swedish scientist Carolus Linnaeus (1707–78) developed a system for naming, ranking, and classifying plant and animal organisms that is still used today. Linnaeus was dubbed the father of taxonomy for his pioneering work Systema Naturae, published in 1735. This work moved beyond the superficial
observations common at the time to provide an anatomically-based classification system of genus and species.
Plant Evolution and Genetics
In the 19th century, plant systematics was developed further through the theory of evolution, as expressed in the 1859 work, On the Origin of Species, by the English naturalist Charles Darwin (1809–1882). This, and the increased interest in plant anatomy, drove an effort to group plants by their phylogenetic, or evolutionary, relationships.
A further understanding of genetics was achieved by Austrian botanist Gregor Mendel (1822–84), who formulated the concept of particulate heredity factors, later called genes. Mendel worked out the basic principles of genetics by observing variations in the floral and vegetative features of garden peas. Although Mendel’s work was little known at the time, its rediscovery at the turn of the 20th century prompted the foundation of the study of genetics.
Today, botanists occupy themselves with a broad range of activities. These range from basic botanical studies, such as forestry and horticulture, to related but more divergent studies, such as agronomy and pharmacology.
Botany is an interconnected series of individual studies. Major botanical studies include the following:
Agricultural science a multidisciplinary field that encompasses those studies used in the practice of farming—producing food, feed, and fuel from the systematic raising of plants for human use.
Agronomy a branch of agricultural science that studies crops and the soils in which they grow.
Economic botany the study of the relationship between people and plants—in particular, the various ways in which people use plants.
Forestry the study and management of forests, plantations, and related natural resources.
Horticulture the culture or growing of garden plants, including plant breeding and genetic engineering.
Paleobotany the study of fossil plants.
Phytopathology the study of plant diseases.
Phytotomy the study of plant structure by dissection (also known as plant anatomy).
Plant ecology the study of the distribution and abundance of plants, and how that is affected by interactions between plants and their environment.
Plant genetics the study of genetic inheritance in plants.
Plant morphology the study of the external structure of plants, in particular the diversity in forms.
Plant physiology the study of the function of plants, including fundamental processes as photosynthesis, respiration, nutrition, and the like.
Plant taxonomy the description and classification of plants.
Pomology the study and cultivation of fruits.
Pteridology the study of ferns.
Plants are a fundamental part of Earth’s life cycle. They generate the oxygen, food, fibers, fuel, and medicine that enable higher life forms to exist. The study of plants has always been crucial to the working of human society. When society understands how plants work, it can use that knowledge to produce food, medicine, and materials that can be used to feed, clothe, and heal its population. A thorough understanding of plant science also helps us to understand changes in the environment, such as global warming.
Nutrition Humans and animals obtain virtually all their food from plants—either directly, by eating fruits and vegetables, or indirectly, by eating animals that rely on plants for their nutrition. Plants are at the base of Earth’s food chain, because they convert energy from the Sun and nutrients from the soil into a form that can be consumed and used by animals. This initial level of the food chain is called the first trophic level.
By studying how plants grow and their role in the food chain, botanists can learn how to increase yields. Increasing yields through selective breeding and genetic manipulation has become integral to providing food security for the growing human population.
Medicine Throughout history, plants have been a key component of humankind’s medicine chest. Many medicinal drugs come directly from plants; other drugs are derived from plant byproducts. Research is ongoing, as future cures for many existing diseases are likely to be derived from plants.
Fuels and Materials Plants provide us with many natural materials used for clothing, construction, and other uses. These materials include cotton, linen, paper, rope, and rubber. Plants are also used to create biofuels, which are likely alternatives to fossil fuels.
The Environment The study of plants also helps us to better understand Earth’s environment. For example, studying plant systematics and taxonomy helps us understand species extinction and habitat destruction. Studying plant life cycles helps us understand climate change, and studying plants’ responses to ultraviolet radiation helps us monitor ozone depletion. In many ways, plants can act as an early warning system, alerting us to important changes in the environment.
Life Processes Plant experimentation poses none of the ethical dilemmas of experimenting on animals, which is why scientists often use plants to study fundamental life processes, such as cell division, genetic inheritance, and protein synthesis. This research typically yields benefits beyond the subject of botany.
The study of plant structure is called plant anatomy, or phytotomy. (This is not to be confused with plant morphology, which is the study of plants’ external structure as used in the field identification of plants.) Most plants contain some or all of the following structural elements.
Flower the reproductive structure of a flowering plant. After the flower has been fertilized, portions of the flower develop into a fruit that contains seeds. The flower structure includes several subparts, including the colorful petals, the sepals (the green areas under the petals, collectively called the calyx), and the gynoecium (the female reproductive part, composed of one or more pistils).
Seed a small embryonic plant. Most plants produce multiple seeds, each encased in a seed coat that contains stored food.
Fruit a hard or fleshy structure that contains the seeds of flowering plants. The fruit is essentially the ripened ovary of a fertilized plant.
Leaf the flat and thin part of the plant responsible for photosynthesis. In most plants, leaves are also responsible for respiration, transpiration, and guttation. They can also store food and water.
Stem the structure that supports the plant’s leaves and fruits and which transports liquids between the roots and other parts.
Bark the outermost layer of stems and roots of woody plants, such as trees.
Root the organ of the plant that bears no leaves and typically lies beneath the surface of the soil. (Some roots can be aerial, however.) Roots exist to anchor the plant body to the ground, absorb water and inorganic nutrients, and in some plants, to store food.
Photosynthesis
Plants are multicellular organisms that carry out photosynthesis, a term meaning to “build with light,” which is how plants convert energy for their own use.
The process of photosynthesis uses the energy of sunlight to convert carbon dioxide and water into the simple sugar glucose. The glucose is then used to build leaves, flowers, fruits, and seeds.
Photosynthesis occurs in specialized cell structures found in leaves and green stems. These structures are called chloroplasts; a single plant leaf might contain 40 to 50 of these cells.
The chloroplast is an oval-shaped structure divided by membranes into numerous disk-shaped compartments, called thylakoids. The membrane of a thylakoid is embedded with hundreds of molecules of chlorophyll, a light-trapping pigment, as well as enzymes and other molecules required for photosynthesis.
There are two stages to plant photosynthesis—the light-dependent reaction, and the light-independent reaction. In the light-dependent reaction stage, the chloroplast traps energy from sunlight and converts it into chemical energy. This chemical energy is stored in two separate molecules: nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP).
In the light-independent reaction stage (formerly called the “dark reaction”), NAPDH provides the hydrogen atoms that help form glucose, while ATP provides the energy for the reactions that synthesize the glucose. This reaction requires the presence of carbon dioxide molecules, which enter the plant via pores in the leaf. During this process, the plant decomposes water into its oxygen and hydrogen atoms; the oxygen is released into the atmosphere while the hydrogen is combined with the carbon and oxygen atoms of the carbon dioxide to form a series of increasingly complex compounds. These compounds eventually evolve into glucose and water.
One important byproduct of the photosynthesis process is oxygen, which is left over when carbon dioxide molecules are rearranged to create glucose molecules during the light-independent reaction. Plants are a major source of the Earth’s oxygen; without photosynthesis, the planet would not have the oxygen-rich atmosphere required for animal life. Conversely, animals are a primary source of carbon dioxide, which plants need to conduct photosynthesis.
All plant life is classified as Kingdom Plantae, which is divided into 12 phyla based largely on the following characteristics:
Tissue structure non-vascular (mosses) and vascular (all other).
Seed structure naked seeds, covered seeds, and spores (reproductive cells capable of reproducing without fusion with another reproductive cell).
Stature mosses, ferns, shrubs and vines, trees, and herbs. The 12 plant phyla are more commonly organized into five major groupings—mosses, ferns, conifers, flowering dicots (two seeds), and flowering monocots (one seed).
Mosses Mosses, liverworts, and hornworts—Bryophyta, Hepatophyta, and Anthoceraphyta—are the only plants that lack a vascular structure for the internal transportation of fluids and nutrients. Instead, they rely on moisture from the surrounding environment. Most mosses are small plants that thrive in moist conditions; they reproduce by means of spores. There are approximately 24,000 species of bryophytes.
Ferns Ferns are vascular plants that transport fluids through their stem structures and reproduce by means of spores. The general category of “fern” includes several distinct phyla—Pteridophyta (ferns), Equisetophyta (horsetails), Lycopodophyta (club mosses), and Psilophyta (whisk ferns), for a total of approximately 15,000 species.
Conifers Conifers are slightly more evolved than ferns; they reproduce by means of seeds instead of spores. The seeds, however, are “naked”—not covered by an ovary. In most conifers, the seed is produced inside a cone-like structure, such as a pine cone. Conifers typically have needle- or scale-like leaves with no flowers.
Conifers are classified in the phylum Gymnospermae. Related phyla include Ginkophyta (Maidenhair Tree), Cycadophyta (cycads), and Gnetophyta (herb-like cone-bearing plants).
Flowering Dicots The vast majority of plants—some 200,000 species—are flowering dicots. This class of angiospermophytes includes most trees, shrubs, vines, flowers, fruits, vegetables, and legumes.
The plants in the phylum Angiospermophyta, class Dicotyledonae, grow their seeds inside an ovary, which is embedded in a flower. After the seed is fertilized, the flower falls away and the ovary swells to become a fruit. Dicots grow two seed leaves.
Flowering Monocots Monocotyledonae, the other class of the phylum Angiospermophyta, are flowering plants that have a single seed leaf. There are around 30,000 monocot species, including grasses, orchids, lilies, irises, and palms. Grain-producing plants are also monocots, including wheat, oats, and corn; fruits such as dates and bananas are also part of the monocot class.
Other Types of Plants
Beyond this formal classification, professional and amateur botanists have additional ways to describe various types of plants. These informal classifications include:
Annual a plant that germinates flowers and dies in a single year. In gardening, an annual is a plant grown outdoors
in the spring and summer that survives for just one growing season.
Bulb a plant that grows from an underground shoot that has modified leaves. These plants, monocots all, include onions, lilies, tulips, and irises.
Fruit a culinary term (not a botanical one) for the seed covering; the means by which edible flowering plants disseminate seeds. When dealing with fruit as food, the term typically refers to those plant fruits that are sweet and fleshy, such as apples, pears, peaches, and oranges.
Grass a type of monocot plant from the family Poaceae. Most grasses are grown for pasture or lawns, or as cereals.
Herb an upright plant without woody stems. Herbs are typically employed for medicinal, culinary, or even spiritual uses.
Nut a type of simple dry fruit with a single seed. The ovary wall becomes very hard at maturity, and some nuts are edible.
Perennial a plant that lives for more than two years.
Shrub also known as a bush, defined as a short (usually less than 15 feet) perennial tree with multiple stems.
Succulent a water-retaining plant, such as the cactus, that has adapted to desert conditions. These plants store water in their leaves, stems, and roots to survive long periods without external moisture.
Tree a woody, perennial plant—typically at least 20 feet high at maturity—with secondary branches supported on a main stem (trunk).
Vegetable a culinary term for the edible part of a plant. Vegetables can include plants with edible leaves (lettuce), stems (asparagus), roots (carrots), flowers (broccoli), bulbs (garlic), and seeds (peas and beans). Generally, if a plant has seeds inside, it is considered a fruit (tomato).
Vine a type of plant that has long, flexible stems, such as the ivies and grape plants.
Water plant a type of plant, woody or not, that has adapted to living in or on aquatic environments.
Wildflower literally a flower that grows wild—that was not intentionally seeded or planted.
The study of plant diseases is called Phytopathology. Plant diseases can be either infectious or non-infectious in nature.
Infectious Diseases
The most common infectious plant diseases include the following:
Bacteria unicellular microorganisms that are ubiquitous in every habitat. Of the approximately trillions of bacterial species, only about 100 cause disease in plants; these plant-harming bacteria are most prevalent in tropical and subtropical regions.
Fungi plant-like organisms that reproduce via spores. Of the 200,000 species of fungi, 10,000 are dangerous to plants; these include biotrophs (which feed on living plant tissue), necrotrophs (which kill plant cells and then feed on the nutrients released), and hemibiotrophs (a hybrid of biogroph and necrotroph).
Nematodes small wormlike creatures that live freely in the soil. Some nematode species in tropical and subtropical regions are parasitic.
Oomycetes also known as water molds. These are microscopic fungal-like organisms that are aggressive plant pathogens.
Parasitic plants plants, such as mistletoe and dodder, that obtain nutrition from other plants.
Viruses microscopic particles that infect the walls of a plant. Most plant viruses do not kill the plant, but only reduce its yield.
Noninfectious Disorders
Other plant disorders are caused not by external organisms, but rather by environmental factors. These physiological plant disorders are exacerbated by factors such as poor light, weather damage (frost, wind, lightning, and the like), too much or too little water, too few nutrients, and pollution. The effects of noninfectious disorders can often be reduced by altering environmental conditions.
Times focus
Green, Life-Giving and Forever Young
By NATALIE ANGIER
Show somebody a painting of a verdant, botanically explicit forest with three elk grazing in the middle and ask what the picture is about, and the average viewer will answer, “Three elk grazing.” Add a blue jay to the scene and the response becomes, “Three elk grazing under the watchful eye of a blue jay.”
We barely notice plants, can rarely identify them and find them incomparably inert. But the antidote to plant apathy is at hand. Botanists urge everyone to venture outside and check out the world through nature’s rose-colored glasses—and the daffodil, cherry blossom, dogwood and lupine ones, too. If this view doesn’t move you, you’re pushing up daisies.
As it happens, plants are not only alive in their own right. They are also the basis of virtually all life on earth, including ours. The core feature of planthood is autotrophy, that is, the happy ability to make one’s own food. Plants essentially eat the sun, transforming solar energy into sugars and starch through the stepwise enzymatic stitchery of photosynthesis.
Moreover, because plants release oxygen as a byproduct of photosynthesis, plants also give us aerobes leave to breathe. Our atmosphere is currently about 20 percent oxygen, all of it the bounty of the planet’s green-skinned autotrophs.
In addition to their caloric self-sufficiency, plants can be envied for their eternal youthfulness. A plant elongates itself through constant cell growth in two zones of its body, at the very tips of the roots, which grow down into soil or other surface to which the plant clings, and the outer tips of the shoots, from which new leaves, flowers and fruits sprout. Whereas an animal, upon reaching maturity, has almost no young cells left in its body.
A plant is also always drinking, slurping water and nutrients the only way it can, through its roots. Everything needs water to survive, but another radical difference between the faunal and floral crafts is that while we can drink water and keep it circulating through the body via the bloodstream, water moves through a plant’s body in a continuous stream, entering through the roots, crawling up the stem and evaporating out through little openings, or stomata, in the leaves. In fact, the upward tug of evaporation is what pulls more water up from the soil, as the clingy water droplets follow each other skyward through the hollow capillaries of the plant’s stem and leaves, shinnying as high as 300 or 400 feet above ground in the case of the giant redwoods.
No, there’s no rest for the weary, especially if you’re immobile. Unable to defend themselves by running away, plants have instead become crackerjack chemists, evolving a vast armamentarium of insect repellents, fungicides, microbicides, ultraviolet blockers and other defensive compounds that human chemists have just begun to tally.
Rootedness also complicates a plant’s love life. Plants, like everybody else, want to spread their seed around and diversify their genetic stock through sexual reproduction, but it’s hard to meet fresh faces when you don’t have legs. A number of plant species like pine trees, oaks, cottonwoods and grasses rely on wind to blow their pollen around, with the hope that some of the male sperm contained therein will land on receptive female parts of their far-flung kind. Or if not the same kind, at least something in the same general group: the boundaries between plant species are far more porous than they are in animals, and different species and even genera of plants cross-hybridize with each other surprisingly often.
Nevertheless, wind sex is highly iffy and inefficient, and many species of modern plants, the angiosperms, instead manipulate members of the animal kingdom to serve as yentas in a more discriminating style. The plants offer up brilliant blossoms to entice a specific pollinating insect or bird, which gets drunk on the blossom’s nectar and wants more and so seeks out other blossoms of similar shape, color or scent. And as the bee or hummingbird flits from one favored flower to the next, it incidentally delivers pollen pockets to just the right spots.
When we eat, we are parasites on the foundational labor of plants; and when we “say it with flowers,” we are plagiarists, too.