Description from Flora of China
Shrubs or trees, deciduous, dioecious, spiny. Leaves alternate, opposite, or whorled, subsessile to petiolate, blade margin entire. Flowers unisexual, clustered at base of lateral shoots. Male flowers in small catkins that appear before the leaves; calyx segments 2, membranous, free; stamens 4; disk small. Female flowers in small racemes, appearing with the leaves; calyx tubular, 2-lobed; style stigmatic on one side. Drupe globose, ellipsoid, or cylindric, sometimes longitudinally ribbed. Seed enclosed in parchmentlike endocarp, sometimes difficult to separate from seed. 2n = 24.
There has been uncertainty in the taxonomy of this genus, reflected in the range of treatments from that of Avdeyev (Izv. Akad. Nauk Tadzh. SSR, Biol. Nauk 4(93): 11-17. 1983), who recognized only one species with two subspecies, to Bartish et al. (Syst. Bot. 27: 41-54. 2002), who suggested on the basis of both morphological and molecular data that there is a good case for recognizing seven species plus a total of ten further subspecies. This latter view is accepted here. Flowering material is relatively rarely collected and the following key is based largely on fruiting material.
Seven species: from NW Europe to E Asia, with a center of diversity on the Qinghai-Xizang plateau, most species associated with seasonally moist situations; seven species (four endemic) in China.