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A genus of a few species of deciduous small trees or shrubs most fully represented in North America, but occurring also in Mexico. The leaves are usually trifoliolate but are sometimes made up of four or five leaflets, aromatic and (with a lens) seen to be covered with pellucid dots. Flowers small. The most distinctive feature of this genus is provided by the fruits, which are thin, flat and broadly winged, rather like hops or elm seed.

Species articles