Trees or shrubs, usually deciduous, rarely evergreen. Leaves simple or compound, opposite, palmately lobed or unlobed-penninerved; petiole bases meeting but not perfoliate, usually exstipulate. Inflorescence corymbose, fasciculate or racemose, lateral or terminal on leafy or leafless shoots. Flowers actinomorphic, perfect or unisexual, rarely dioecious. Sepals and petals 4-5, rarely absent. Stamens 4, 6, 8, 10 or 12, inserted inside or outside the disc. Ovary bicarpellate, transversely compressed, bilocular, each locule biovulate; stigma usually bifurcate, rarely absent. Fruit a geminate samara; mericarps indehiscent.
A bigeneric family of temperate North America, N.W. Africa, Europe, Asia and Indonesia. Acer is found in Pakistan. The other genus, Dipteronia, is endemic to central China.
Acknowledgements: We are grateful to the United States Department of Agriculture for financing this research under P.L. 480.
