Notes on Pappophorum (Gramineae: Pappophoreae)

Abstract

The American genus Pappophorum, with species in both Northern and Southern hemi- spheres, has been a source of considerable taxonomic confusion. During the past two decades, various agrostologists have estimated the number of species to be from 9 to 20. Not only has there been disagreement regarding the number of species, the application of various binomials has differed among specialists who have studied the group. Three names that have continued to be applied in different senses are: P. mucronulatum, P. subbulbosum, and P. vaginatum Buckley, non Philippi. For many years the name P. mucronulatum was applied to plants from both North and South America, and P. subbulbosum and P. vaginatum were relegated to synonymy under that name. Some recent botanists have held that only P. pappiferum and perhaps P. subbulbosum are amphitropic, whereas P. vaginatum is restricted to North America, and P. mucronulatum and P. subbulbosum, both distinct species, occur only in South America. Authors of the present study recognize only eight species for the genus. Pappophorum mucronulatum is treated as a South American species, which is restricted to Brazil, Colombia, and Venezuela. Pappophorum vaginatum, with P. subbulbosum as a synonym, occurs in the southwestern United States and Mexico, and also in Argentina and Uruguay. A key to the species along with the important synonymy is provided. Pappophorum Schreber is an American genus, with the majority of taxa in the Southern Hemi- sphere. The range in South America is from Colombia and Venezuela, south through Ec- uador, Peru, Bolivia, and Brazil to Paraguay, Argentina, and Uruguay, and in North America from Mexico to southwestern U.S.A. Estimates regarding the total number of species have var- ied from 12 (Burkart 1969) to 20 (Cabrera 1970; Nicora 1978). Pensiero (1986), the most recent South American author to deal with Pappopho- rum, listed the number as approximately 10, which is in essential agreement with Clayton and Renvoize (1986), who gave the number as nine. Hitchcock (1913), in his treatment of the Mex- ican grasses, listed three species under Pappo- phorum. One of these, P. wrightii S. Watson, is a