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Any plant of the genus Nicotiana cultivated for its leaves, and the dried leaves of the plant. Most often, tobacco means a leaf product derived from the plant genus Nicotiana containing 1–3% of the alkaloid nicotine, which produces a narcotic…

Pathological conditions affecting shade and forest trees. Diseases of both shade and forest trees are caused by the same pathogens, but the trees differ in value, aesthetics, and utility. In forests, disease is significant only when large numbers…

The common name for fern plants primarily belonging to the families Cyatheaceae and Dicksoniaceae, whose members typically develop tall trunks crowned with leaves (fronds). Tree ferns exhibit a treelike (arborescent) habit (Fig. 1), often reaching…

The study of systems consisting of arbitrary sets of elements of unspecified type, together with certain operations satisfying prescribed lists of axioms. Abstract algebra has been developed since the mid-1920s and has become a basic idiom of…

Few fossils of early flowering plants (angiosperms; Magnoliophyta) have been found. The group appears suddenly in the fossil record and quickly rose to ecological dominance. As a result, Charles Darwin famously referred to the origin of angiosperms…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Arecidae of the class Liliopsida (monocotyledons). The order Arales consists of two families: Araceae, with about 1800 species; and Lemnaceae, with only about 30…

An area set aside for the cultivation of trees and shrubs for educational and scientific purposes. An arboretum differs from a botanical garden because the former emphasizes woody plants; in contrast, a botanical garden includes investigation of the…

A tree or shrub, sometimes called the tree of life, belonging to the genus Thuja of the order Pinales. Arborvitae is characterized by flattened branchlets with two types of scalelike leaves. At the edges of the branchlets, the leaves may be keeled…

An order of flowering plants, division Magnoliophyta (Angiospermae), of the subclass Arecidae in the class Liliopsida (monocotyledons). The name of the subclass is derived from the ordinal name. The order consists of the single family Arecaceae…

A subclass of the class Liliopsida (monocotyledons) of the division Magnoliophyta (Angiospermae), the flowering plants, consisting of four orders (Arecales, Cyclanthales, Pandanales, and Arales), five families, and nearly 6000 species. Except for…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Magnoliidae of the class Magnoliopsida (dicotyledons). It contains only the family Aristolochiaceae, with 8 or 10 genera and about 600 species, most of them in…

Cynara scolymus (alternatively Cynara cardunculus var. scolymus), a herbaceous perennial plant, in the family Compositae (order Asterales), whose flower head is edible. The artichoke, also called the globe artichoke, has its origin in the…

A genus, Fraxinus, of deciduous trees of the olive family Oleaceae, order Lamiales. Ash trees have opposite, pinnate leaflets (see illustration), except in one species, F. anomala, which has only a single leaflet. About 65 species are found in the…

A large, widespread order of petaloid monocotyledons consisting of 29 families and about 26,000 species. Asparagales are clearly circumscribed in deoxyribonucleic acid (DNA) sequence analyses but are difficult to define morphologically, and…

A dioecious perennial monocot (Asparagus officinalis) of Mediterranean origin belonging to the plant order Asparagales. Asparagus is grown for its young shoots or spears, which are canned, frozen, or cooked fresh as a vegetable. These aerial stems…

An order of flowering plants, division Magnoliophyta (Angiospermae), which gives its name to the subclass Asteridae in the class Magnoliopsida (dicotyledons). The Asterales have often been included in the order Campanulales, but they are perhaps…

A large subclass of the class Magnoliopsida (dicotyledons) of the division Magnoliophyta (Angiospermae), the flowering plants, consisting of 11 orders, 49 families, and more than 60,000 species. The Asteridae are mostly sympetalous with unitegmic,…

A small extinct order of the class Lycopsida that bridges the evolutionary gap between the primitive Zosterophyllopsida and relatively advanced Lycopsida. Members of the order Asteroxylales (asteroxylaleans) are often termed prelycopsids. The…

Any of a class of plant growth substances (phytohormones or plant hormones) that have an essential role in coordination of many growth and developmental processes during the life cycle of plants, especially the ability to increase the rate of shoot…

A tropical and subtropical evergreen tree, Persea americana, in the Lauraceae family (containing also the laurel of antiquity and the trees that yield commercial cinnamon and camphor), which bears a pulpy pear-shaped edible fruit. The avocado…

A large tropical plant of the genus Musa and its edible fruit. The banana belongs to the family Musaceae. The banana of commerce (Musa acuminata), which is believed to have originated in the Asian tropics, was one of the earliest cultivated fruits.…

A word generally referring to the surface region of a stem or a root. The term has a variable meaning, and sometimes part or all of the bark is called rind. Occasionally the word is used as a substitute for periderm or for cork only. Most commonly,…

An important grass plant of the genus Hordeum that is cultivated as a grain crop and whose seed is used as a cereal and to manufacture malt beverages. Barley (Fig. 1) is grown in nearly all cultivated areas of the temperate parts of the world and…

An annual herb (Ocimum basilicum) of the mint family (Lamiaceae; also known as Labiatae), grown from seed for its highly scented leaves. Basil is sold fresh or dried, and its essential oil is used in pharmaceuticals and flavoring. The genus Ocimum…

A member of the linden tree family (Tiliaceae) in the order Malvales. One species is known as the American linden or basswood (Tilia americana) [see illustration]. Basswood is a timber tree of the northeastern quarter of the United States and the…