SCLEROPOGON (GRAMINEAE) , A MONOTYPIC GENUS WITH DISJUNCT DISTRIBUTION John R. Reeder &-L. J. Toolin Herbariiun, University of Arizona, Tucson, AZ 85721 Abstract Examination of herbarium specimens of Scleropogon from both North and South America, along with field work in southern Arizona, has confirmed the long-held view that the genus is monotypic. Our studies failed to substantiate the existence in southwestern U.S. and Mexico of a distinct entity, marked by a coherent suite of characters, that is specifically distinct from Scleropogon brevi-folius as it exists in South America. S. longisetus Beetle is, therefore, reduced to synonymy. The genus Scleropogon was established by Philippi (1870), based on material collected in the vicinity of Mendoza, near the border between Argentina and Chile. The type species is S. brevifolius. Urtil 1981, when A. A. Beetle described a second species, Sciero-pogon was considered to be monotypic, having a disjunct distrib-ution with populations in both North and South America. The plants are diclinous, having unisexual flowers which may be borne on the same or different plants. Moreover, the staminate and pistillate spikelets are quite different, the lemmas of the former having short awns, or none, whereas the latter are long awned. In describing his new species, Scleropogon longisetus (based on Reeder s Reeder 3626 from Coahuila, Mexico) Beetle (1981) stated that it was confined to North America, in contrast to S. brevifolius, which occurs in both the Northern and Southern Hemispheres. He includes the following key: "Dioecious, rhizomatous, the panicles scarcely exserted above the leaves, the awns 3 — 5 cm long, at maturity twisted and strongly recurved Scleropogon brevifolius Monoecious, stoloniferous , the panicles well exserted above the leaves, the awns 5 — 15 cm long, twisted but not strongly recurved Scleropogon longisetus" (Although in his key, Beetle gives the awn length for S. brevi-folius as 3 — 5 cm, in his description it appears as "5 — 15 cm"!) Botanists familiar with "dioecious" plant species will know that this condition is somewhat fragile. In a number of such grasses (e.g. Buchloe, Opizia, Pringleochloa) staminate and pistillate inflorescences may occur on the same plant within populations in which other plants of the same species bear either cf or 9 flowers , but not both. That the well-known and wide-ranging genus Scleropogon , consid-ered to be monotypic since it was originally described, actually 267
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