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 in the Andes of South America. They have a smooth gray bark; elliptical or ovate saw-toothed leaves in three rows; male flowers in long catkins, mostly in early spring; and clusters of several dry, hard, ellipsoid blackish fruits that are 0.5–1 in. (1.25–2.5 cm) in length. The fruits are conelike and present throughout the year. Alders are common in wet soils, such as stream borders. They often form thickets even beyond treelines and are pioneers on bare areas (including landslides and roadsides) and after fire or logging. As in legumes, the roots bear swellings or nodules containing nitrogen-fixing bacteria, which enrich the soil. See also: Fagales; Nitrogen fixation; Nitrogen-fixing trees

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 Northern Hemisphere. The ash tree occurs in America south to Mexico, in Asia south to Java and in Europe. See also: Lamiales; Tree

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. This fast-growing tree is indigenous to the tropical regions of the Americas, from southern Mexico to Bolivia. In particular, Ecuador is the world's leading producer of balsa wood. The leaves of balsa (see illustration) are simple, angled, or lobed. The flowers are large and yellowish-white or brownish, and they are terminal on the branches. See also: Forest; Forestry; Malvales; Tree

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 adjacent area of Canada and grows to a height of 120 ft (36.5 m). The leaves are heart-shaped, coarsely toothed, long, pointed and alternate. See also: Malvales; Tree

A genus, Fagus, of deciduous trees of the family Fagaceae in the order Fagales. Beech trees can be distinguished by their long (often more than 1 in. or 2.5 cm), slender, scaly winter buds; their thin, gray bark, which is smooth even in old trees; and their simple, toothed, ovate or ovate-oblong, deciduous leaves (Fig. 1). See also: Fagales; Tree

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, hornbeams, and hophornbeams) in the order Fagales. Approximately 40 species of birch are known. The sweet birch (B. lenta), yellow birch (B. alleghaniensis), and paper birch (B. papyrifera) [Fig. 1] are all important timber trees of the eastern United States. Both the yellow and paper species extend into Canada. The gray birch (B. populifolia) is a smaller tree of the extreme northeastern United States and adjacent Canada. The river (black) birch (B. nigra) is a less common tree of wet soils and banks of streams; it is important as an ornamental tree and is often planted for erosion control. See also: Alder; Deciduous plants; Erosion; Fagales; Forest; Forest timber resources; Forestry; Hophornbeam; Hornbeam; Ornamental plants; Tree

A genus, Aesculus, of deciduous trees or shrubs belonging to the plant order Sapindales. Buckeyes grow in North America, southeast Europe and eastern Asia (including India). The distinctive features of buckeyes are opposite, palmately compound leaves and a large fruit having a firm outer coat and containing usually one large seed with a conspicuous hilum [the scar on a seed marking the point of detachment from the funiculus (stalk of an ovule)]. The Ohio buckeye (A. glabra) [see illustration], a small tree that may grow to a height of 9 m (30 ft), is found mainly in the Ohio valley and in the southern Appalachians. It can be recognized by glabrous (smooth) winter buds, prickly fruits that are 2.5–5 cm (1–2 in.) in length and compound leaves that have five leaflets. See also: Forest and forestry; Sapindales; Tree

The tree Cinnamomum camphora, a member of the laurel family, from which camphor is extracted. The camphor tree (see illustration) belongs to the Lauraceae (laurel) family of plants in the order Laurales. It is a native species of China, Japan, and Taiwan. The tree grows typically to a height of 12 m (39 ft), is dense-topped, and has shiny, dark, evergreen leaves. It is widely planted as an ornamental tree or a timber tree. The Janka hardness for the wood from the camphor tree is 422 kg-force (930 lb-force); its density is 625 kg/m³ (39 lb/ft³). All parts of the tree contain camphor (a terpene ketone). Camphor oil (an essential oil) is obtained by steam distillation of finely ground wood from the camphor tree. During the distillation process, the crude camphor crystallizes on the surface of the still. After the camphor is removed and refined, it is the commercial gum camphor, which is used in medicines and perfumes, as well as in the manufacture of celluloid and nitrocellulose compounds. See also: Camphor; Essential oils; Forest timber resources; Laurales; Ornamental plants; Tree

Any of a large number of evergreen trees having fragrant wood of great durability. Chamaecyparis thyoides is the botanical name of the southern white cedar, which may grow to a height of 22 m (72 ft). It is characterized by small, spherical cones with peltate, seed-bearing scales fitted together to form a little ball and by small scalelike evergreen leaves (Fig. 1). It grows only in swamps near the eastern coast of North America, where it is also known as Atlantic white cedar. The wood is soft, fragrant and durable in the soil and is used for boxes, crates, small boats, tanks, woodenware, poles and shingles. Arborvitae is sometimes called northern white cedar. See also: Arborvitae; Evergreen plants; Forest and forestry; Pinales; Tree

Any of seven species of deciduous, nut-bearing trees of the genus Castanea (order Fagales). Chestnut trees are native to the Northern Hemisphere and have been introduced throughout the world. The nuts of chestnut trees are actually fruits, with the shells enclosing cotyledons. Trees bear both male and female flowers in late spring, but must be cross-pollinated for nut production. Nuts are borne in a spiny involucre or burr that opens to release the nuts in late fall. See also: Forest and forestry; Fruit; Nut crop culture; Tree