Description from Flora of China
Trees or rarely shrubs, deciduous or rarely evergreen. Leaves odd-pinnate, opposite or rarely whorled at branch apices; petiole and petiolule often basally thickened. Inflorescences terminal or axillary toward end of branches, or lateral on branches of previous year, paniculate; bracts linear to lanceolate, caducous or absent. Flowers small, unisexual, bisexual, or polygamous. Calyx 4-toothed or irregularly lobed, sometimes absent. Corolla white to yellowish, 4-lobed, divided to base or absent. Stamens 2, inserted at base of corolla lobes; filaments short, exserted at anthesis. Ovules 2 in each locule, pendulous. Style short; stigma ± 2-cleft. Fruit a samara with apically elongated wing. Seeds usually 1, ovate-oblong; endosperm fleshy; radicle erect.
About 60 species: mostly in temperate regions and subtropics of the Northern Hemisphere; 22 species in China.
Some species are widely used in China for commercial timber and the bark for medicinal drugs.
(Authors: Wei Zhi; Peter S. Green)