Monoecious or more rarely dioecious, usually deciduous trees or shrubs. Lvs opposite, exstipulate, simple, usually palmately toothed or lobed, less commonly pinnately compound with up to 15 leaflets. Fls actinomorphic, small, hypogynous or perigynous, arranged in fascicles, corymbs, racemes or panicles. Sepals 4-5. Petals usually 4-5, sometimes 0. Stamens (4)-8-(10), inserted on or inside the usually well-developed disc. Ovary superior, 2-celled, compressed, with septum along the short axis; ovules 2 in each cell; styles 2, free or united below. Fr. schizocarpic, splitting into 2 samaras; wing on upper side or occasionally extending round the seed. Seed non-endospermic; cotyledons flat or plicate, often green.