Phylogenetic Relationships of the Decumbentes Group of Paspalum, Thrasya, and Thrasyopsis (Poaceae: Panicoideae: Paniceae)

Paspalum (Poaceae: Panicoideae: Paniceae) includes 330 species distributed mainly in tropical and subtropical regions of America. Due to the large number of species and convergence in many characters, an adequate infrageneric classification is still needed. Studies on Paniceae based on molecular and morphological data have suggested that Paspalum is paraphyletic, including the genus Thrasya, but none of these analyses have included a representative sample of these two genera. In this study, phylogenetic relationships among the informal group Decumbentes of Paspalum, plus subgenera and other informal groups, and the genera Thrasya and Thrasyopsis were estimated. A cladistic analysis under parsimony was performed using a matrix of 50 taxa and 77 morphological and anatomical characters. Different analytical parameters were explored, equally weighing characters and employing implied weights by varying the concavity constant, k, from I to 12. Almost all analyses showed that species of the Decumbentes group and Thrasya form a natural group, supported by the presence of axillary peduncles in the upper foliar sheath, the upper glume slightly shorter than the spikelet, margins of the lower lemma plicate on the upper anthecium, and the upper anthecium without simple papillae. The position of Thrasyopsis is not clear because it varies within the different analyses. The most important clades are discussed as well as diagnostic characters usually employed to distinguish the genera.