Subfamily Chloridoideae has a history of unsettled taxonomic problems at the tribal and generic levels, and phylogenetic relationships within and among its tribes are not well understood. DNA sequences of the plastid gene matK for 74 species representing 56 chloridoid genera and all tribes and subtribes were used to reconstruct a phylogeny for the subfamily. The base of the Chloridoideae clade shows a polytomy among Triraphis schlecteri and three strongly supported clades labeled A, B, and C. Clade A comprises the Pappophoreae, Uniolinae, and three genera of Eragrostideae; clade B includes most representatives of subtribe Sporobolinae, Spartina, Zoysia, and two Eragrostis species; and clade C encompasses the remaining species. The two largest tribes Eragrostideae and Chlorideae appear polyphyletic. The traditional Pappophoreae minus Pappophorum comprise a clade corresponding to the Cotteinae; Pappophorum nests within a sister clade. The Uniolinae, Orcuttieae, and Triodiinae form strongly supported monophyletic entities. Two large genera, Chloris and Eragrostis, do not appear monophyletic. A pattern of segregation of Old World from New World species is evident in several clades. These results provide a framework for further studies at the tribal and generic levels moving toward a comprehensive systematic treatment of the Chloridoideae.

Communicating Editor: Jeff H. Rettig