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white alder, deciduous shrub or small tree (Clethra alnifolia) native to the Appalachians, named for the resemblance of its leaves to those of the unrelated true alders. It is cultivated as an ornamental for the fragrant white or pinkish blossoms. Similar in appearance and also cultivated are the sweet pepper bush, or summer sweet (C. acuminata), of a somewhat wider range, and a Japanese species (C. barbinersis), whose young leaves are eaten with rice by peasants in its native localities. Most other Clethra species are of tropical America. They are good honey plants. White alder is classified in the division Magnoliophyta, class Magnoliopsida, order Ericales, family Clethraceae.

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alder

alder, name for deciduous trees and shrubs of the genus Alnus of the family Betulaceae (birch family), widely distributed, especially in mountainous and moist areas of the north temperate zone and in the Andes. The black alder (A. glutinosa) is an Old World species now naturalized in E North America. Its bark, still used for dyes and tanning, was formerly considered medicinal; its wood is useful chiefly as charcoal. A. rugosa, the speckled alder, forms extensive swamp thickets in Eurasia and North America. The red alder (A. rubra), the largest tree of the genus, is the most important hardwood timber tree in its native region, the Pacific coast of North America. Alder trees are classified in the division Magnoliophyta, class Magnoliopsida, order Fagales, family Betulaceae.

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Alder, Kurt

Alder, Kurt, 1902-58, German chemist, educated at Berlin and at Kiel. He was on the research staff of the Bayer Dye Works (1936-40) before becoming (1940) professor of chemistry and director of the chemical institute of the Univ. of Cologne. He shared with Otto Diels the 1950 Nobel Prize in Chemistry for discovering a process for the synthesis of complex organic compounds. The Diels-Alder reaction in its simplest form is the reaction of an alkene with a diene to form a cyclohexene.

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alder

Alder (Alnus glutinosa)

Any of about 30 species of ornamental shrubs and trees in the genus Alnus, of the birch family, found throughout the Northern Hemisphere and western South America on cool, wet sites. Alders are distinguished from birches by their usually stalked winter buds and by cones that remain on the branches after the small, winged nutlets are released. Alders have scaly bark, oval leaves that fall without changing colour, and separate male and female flowers (catkins) borne on the same tree. Some familiar North American alders are the red alder (A. rubra or A. oregona); the white, or Sierra, alder (A. rhombifolia); and the speckled alder (A. rugosa). Alder wood is fine-textured and durable, even under water; it is useful for furniture, cabinetry, and lathe work and in charcoal manufacture and millwork. Alders' spreading root systems and tolerance of moist soils lend them to planting on stream banks for flood and erosion control.

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