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An order of the plant class Pinopsida (Coniferopsida) within the division Pinophyta (Gymnospermae). All members of the Pinales, often termed conifers, are woody plants. They comprise trees or shrubs, and are often the principal trees of the forests…

A plant, Musa textilis, of the banana family that is valuable for its hard fiber (also known as Manila hemp) and native to Borneo and the Philippines. Abaca is one of the strongest of the hard fibers. Commercially, it is known as Manila hemp. The…

One of the major plant hormones that plays an important role in plant growth and development. Abscisic acid (ABA) is ubiquitous in vascular plants; the highest levels are found in young leaves and in developing fruits and seeds. Abscisic acid is…

The process whereby a plant sheds one of its parts. Leaves, flowers, seeds, and fruits are parts commonly abscised. Almost any plant part, such as very small buds and bracts to branches several inches in diameter, and scales or sheets of bark, may…

A major constituent of the cell walls of certain red algae, especially members of the families Gelidiaceae and Gracilariaceae. Extracted for its gelling properties, it is one of three algal polysaccharides of major economic importance, the others…

Any of the deciduous shrubs and trees of the genus Alnus in the birch family (Betulaceae). There are approximately 30 species of alder, with 10 in the United States. Alders are widespread in cool north temperate regions and are also found southward…

The world's most valuable forage legume, Medicago sativa, also known as lucerne, and less often as purple medic, medica, snail clover, median herb, Burgundy hay or clover, and Chilean clover. Alfalfa is often referred to as the queen of forages. It…

A major constituent (10–47% dry weight) of the cell walls of brown algae. Extracted for its suspending, emulsifying, and gelling properties, it is one of three algal polysaccharides of major economic importance, the others being agar and…

A small order of flowering plants, division Magnoliophyta (Angiospermae), which gives its name to the subclass Alismatidae of the class Liliopsida (monocotyledons). It consists of three families (Alismataceae, Butomaceae, and Limnocharitaceae) and…

A relatively primitive subclass of the class Liliopsida (monocotyledons) of the division Magnoliophyta (Angiospermae), the flowering plants, consisting of 4 orders, 16 families, and less than 500 species. Typically they are aquatic or semiaquatic,…

An annual plant (seldom perennial) of the genus Amaranthus (family Amaranthaceae) that is distributed worldwide in warm and humid regions. Amaranth plants are botanically distinguished by their small chaffy flowers (see illustration), which are…

A class of the plant division Bryophyta, containing plants commonly called granite mosses. The class consists of one order and two families, the Andreaeobryaceae and the Andreaeaceae. The large tapered foot and short, massive seta of the…

A small class of the plant division Bryophyta, made up of plants commonly called hornworts. There is a single order with six genera. Gametophyte structure The gametophytes are flat thalli, often forming rosettes of uniform thickness (see…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Rosidae of the class Magnoliopsida (dicotyledons). The order Apiales (also known as the Umbellales) includes two major families: the Apiaceae, with about 3500…

Correlative inhibition of the growth of lateral (axillary) shoots exerted by the growing apical bud of the plant stem. Competition for growth occurs between plant parts. Strongly growing fruits and branches (organs) act as sinks that divert energy…

Permanently embryonic tissue involved in cell division at the apices of roots and stems, and forming dynamic regions of growth. These apical meri­stems, usually consisting of small, densely cytoplasmic cells, become established during embryo…

A deciduous tree, Prunus armeniaca, in the order Rosales that produces a simple fleshy stone fruit. The apricot is thought to be native to China; then it was distributed throughout Asia and Europe, and eventually North America, South America, and…

A class of nonflagellate unicellular algae, commonly called diatoms, with boxlike silicified walls. Diatoms range in maximum dimension from 4 micrometers to more than 1 millimeter. The diatom wall or frustule (Fig. 1) comprises several interlocking,…

A fast-growing tree, Ochroma pyramidale (also known as O. lagopus), which is widely distributed in tropical America, especially in Ecuador. Balsa (Ochroma pyramidale; also, O. lagopus) belongs to the mallow family, Malvaceae, in the order Malvales.…

Fungi that exhibit the natural phenomenon of bioluminescence (the ability of an organism to emit visible light). Bioluminescence is the emission of photons of visible light by living organisms via the chemical reaction of molecular oxygen (O2) with…

A deciduous tree of the genus Betula, which is distributed over much of North America, in Asia (south to the Himalayas), and in Europe. Birch trees are assigned to the genus Betula. They belong to the family Betulaceae (which also contains alders,…

A group of steroidal plant hormones, typified by the compound brassinolide, that produce effects on plant growth and development. Plant hormones are naturally occurring organic molecules that regulate multiple aspects of plant growth and development…

A genus comprising yeastlike fungi that cause a variety of human diseases referred to as candidiasis. All Candida species are single-celled yeasts that are ovoid in shape and 3–5 μm in size, and they multiply by a process called budding. Most of…

Common pigments, typically of yellow, orange, or red hues, that serve in both light absorption and the protection against too much light in photosynthesis as well as in the vision process. Carotenoids comprise a class of labile, easily oxidizable,…

Specialized structures found in plant cells, diverse in distribution, size, shape, composition, structure, function, and mode of development. Types A number of different types is recognized. Chloroplasts occur in the green parts of plants and are…

Complex structural matrices surrounding all plant cells. Plant cell walls consist mostly of polysaccharides, but they also contain components such as lignin, structural lipids, and proteins in specialized cell types. However, the term plant cell…

A linear polymer of (1→4)-linked β-d-glucopyranosyl units, and the most abundant of all naturally occurring substances. Cellulose is the main polysaccharide in living plants, forming the skeletal structure of the plant cell wall. Cellulose…

The generic name for any of the intensely green, blue, or purple pigments found in higher plants, algae, and photosynthetic bacteria that are an integral part of photosynthesis. Chlorophyll is the name given to any member of a group of important…

A tropical evergreen shrub or small tree of the genus Coffea (family Rubiaceae), a native of northeast Africa and adjacent southwest Asia, cultivated for the seeds (coffee beans) of its fruit. Members of the genus Coffea (Fig. 1) grow mainly between…

Zea mays, also known as maize, a grain crop grown for its edible seeds (kernels). Corn (Zea mays) [Fig. 1] is an important cereal grass plant belonging to the order Poales (formerly Cyperales). The top corn-producing countries are the United…

A blue/ultraviolet-A (UV-A) light receptor found in a wide range of organisms from bacteria to humans. Cryptochrome was so named because early studies were largely done with cryptogamic (flowerless) plants and because its molecular nature once…

A warm-season annual cucurbit (Cucumis sativus), originally native to India, which is grown for its edible, immature, fleshy fruit. The cucumber is originally native to India and is grown for its edible, immature, fleshy fruit (Fig. 1). The cucumber…

Volatile, fragrant oils obtained from plants. Essential oils are distinguished from those known as fixed oils, which are mainly triglycerides of fatty acids. Essential oils have been obtained from thousands of plants (Fig. 1) and are designated and…

An alkene, formula CH2=CH2. Ethylene (see illustration) is a colorless gas with a boiling point of −103.8°C and a melting point of −169°C. Ethylene is the most-produced organic chemical in the world and is used to make hundreds of products as well…

A taxonomic domain consisting of the vast array of living and fossil organisms with complex cells in which the genetic material is organized into chromosomes [linear pieces of deoxyribonucleic acid (DNA) bound with histone proteins and visible as…

The application of biotechnological techniques utilizing fungi for agricultural purposes. Fungal biotechnology is applied in agriculture to promote plant vigor, to increase yields, and to reduce impacts of plant diseases, weeds, or invertebrate…

Pathological conditions resulting from invasion by pathogenic fungi. Fungi are microorganisms that fill many natural niches in nature. They form a diverse group of eukaryotic microorganisms, including an estimated 2.2 to 3.8 million different…

A eukaryotic kingdom of organisms consisting of the principal decomposers of ecosystems. Fungi are nucleated, usually filamentous, spore-bearing organisms devoid of chlorophyll. Although approximately 100,000 species have been described in the…

The only order of the class Gnetopsida in the division Gnetophyta. There are three living families, each with a single genus: Ephedraceae (Ephedra; 65 species in arid regions), Gnetaceae (Gnetum; 29 species in the tropics), and Welwitschiaceae…

The common name for about six species of thorny, spreading bushes of the genus Ribes, producing small, acidic, edible fruits. Gooseberries and currants all belong to the genus Ribes (order Saxifragales or Rosales, depending on the classification…

A glass- or plastic-enclosed structure that is used to grow plants under protected conditions. Greenhouses (also known as glasshouses) are transparent, enclosed, climate-controlled structures (Fig. 1) in which young, tender, or out-of-season plants…

A long-keeping cultivar of muskmelon, Cucumis melo inodorus, of the gourd family. Honey Dew melons (see illustration) are members of the family Cucurbitaceae (which includes melons, squashes, pumpkins, and cucumbers) in the order Cucurbitales; they…

An order of the true mosses (subclass Bryidae). Also known as the Hypnobryales, this order consists of 14 families and some 135 genera, primarily put together because they share a hypnoid peristome (as described below). The families show…

Bipartite, intimate, and mutualistic symbioses that are formed by soil-inhabiting fungi and plants. Mycorrhizae (mycorrhizas) can be formed between different groups of fungi and the roots, rhizomes (underground horizontal shoots), or thalli (plant…

A ground tissue chiefly concerned with the manufacture and storage of food. The primary functions of plants, such as photosynthesis, assimilation, respiration, storage, secretion, and excretion—those associated with living protoplasm—proceed mainly…

A chemical of biological origin, other than an enzyme, that plays an important causal role in a plant disease. Most pathotoxins are produced by plant pathogenic fungi or bacteria, but some are produced by higher plants, and one has been reported to…

An annual leafy leguminous vine, Pisum sativum (order Fabales), cultivated for its smooth or wrinkled, round edible seeds, which are borne in dehiscent pods. The garden pea is one of the world's oldest cultivated crops. It is a native of western…

A deciduous fruit tree species, Prunus persica, of the order Rosales that originated and was first cultivated in western China. The peach (see illustration) is adapted to relatively moderate climates in the temperate zone. Although most peach…

A low-branching, self-pollinated, one- to six-seeded annual legume (Arachis hypogaea) cultivated for its edible seed, which forms beneath the soil in a pod. Peanuts are cultivated throughout the tropical and temperate climates of the world. Peanut…

Any of approximately 20 species of deciduous trees, and their fruits, in the genus Pyrus (order Rosales). About half of the species of pear are native to Europe, North Africa, and the Middle East, especially areas around the Mediterranean Sea; the…