Shrubs or occasionally clambering vines. Branches jointed, yellowish green to olive-green when young. Leaves opposite or in whorls of 3, apex obtuse to setaceous from an adaxial-median thickening. Pollen cones lanceoloid or ellipsoid to ovoid or obovoid. Seed cones ellipsoid to ovoid, obovoid, or nearly globose. Seeds ellipsoid to globose, yellow to dark brown, smooth to scabrous or furrowed. x = 7. The species of Ephedra are presented here in alphabetical order for three reasons. First, no modern monographic treatment has been written for all species of the genus since that of O. Stapf (1889). Second, it appears that the species occurring in North America belong to at least three wholly different groups within the genus, but this is not yet supported by thorough systematic studies. Third, interspecific relationships within any putative infrageneric group occurring in North America are at best vague and ill defined. The North American species of Ephedra are well defined based on combinations of vegetative and reproductive characters. Putative hybrids reported and described by H. C. Cutler (1939) appear to be products of singular events; these hybrids are discussed under the parental species. Infraspecific taxa are not recognized in this treatment because there appear to be no consistent defining characters and no geographic correlations; previous recognition of infraspecific taxa (H. C. Cutler 1939) appears to be based on random variability.