| Abstract: | This revision discusses the 10 species of Eriogonum assigned to the subgenus Pterogonum. Six of the species are essentially restricted to northern Mexico; two additional species, E. hemipterum and E. nealleyi, are found primarily in Texas; and the remaining two, E. hieracifolium and E. alatum, are the most widespread species of the subgenus being found mainly in the United States and just barely entering Mexico. The subgenus is characterized by the broad, often winged or ribbed achenes, and the generally erect habit of the stems of these perennial herbs. Three new species, E. fimbriatum, E. viscanum, and E. clivosum, are described. They are related to E. ciliatum and are found in the desert foothills of north central Mexico. Two new varieties of E. atrorubens are proposed. One, var. nemorosum, is restricted to the high mountains of the Sierra Madre Occidental in northern Durango and southern Chihuahua, while the second, var. auritulum, is a plant of the Sierra Madre Oriental of Coahuila and Nuevo León. The subgenus is divided into four sections, two of which, Peregrina and Astra, are new. Cytological information is given for nearly all taxa and shows the majority of species to have a haploid number of 20. Eriogonum atrorubens var. intonsum is a polyploid with n = 40, and E. greggii is the most unusual with a haploid number of 16. Each species is described in detail, discussed, and illustrated. Distribution maps are given noting the known locations for each taxon. |
