Syn. Gen. Compos.,194. 1832
w North America, Mexico, Central America (Guatemala).
Gymnosperma is an abundant element of the dry upland flora from the southwestern United States through Mexico to Guatemala, recognized by its shrubby habit, resinous stems, leaves, and heads, small heads in dense, terminal corymbiform arrays, few and inconspicuous rays, and epappose cypselae. It differs from Gutierrezia in its tendency to produce cylindric heads, glabrous receptacles, ray florets with short laminae, and more reduced pappi.
Gymnosperma, Gutierrezia, Amphiachyris, and Thurovia apparently constitute a monophyletic group (M. A. Lane 1982; Y. Suh and B. B. Simpson 1990; G. L. Nesom 1993b), sharing small heads with few florets, similar phyllaries, reduced pappi, reduced chromosome numbers, and similar geographies. Gymnosperma is the basal element in this group; its chromosome number (2n = 16) may be tetraploid (based on x = 4, with a similar marked reduction from x = 9, like those of its close relatives); or it may be diploid (based on x = 8, still a reduction from x = 9). Lane (1996) suggested that the closest relative of Gymnosperma is the Caribbean genus Gundlachia A. Gray (x = 9), citing vegetative and reproductive similarities.