Systematic revision of the subgenus Harpostachys of Paspalum (Poaceae: Panicoideae: Paniceae).

A systematic revision of Paspalum subg. Harpostachys is presented. Different authors have related species of the informal Decumbentes species group of Paspalum to genus Thrasya, on the basis of these morphological characters: the presence of terminal and axillary inflorescences in the upper foliar sheaths, solitary racemes, the presence of lower glumes, and a staminate lower flower. Through a recent phylogenetic analysis using morphological and anatomical characters, Denham and Zuloaga concluded that the species of the Decumbentes group and the species of genus Thrasya constitute a monophyletic group; this result is in agreement with previous molecular phylogenetic studies in the subfamily Panicoideae. In this study, the 22 species of Thrasya are transferred to Paspalum; six new species names and 15 new combinations are proposed: Paspalum achlysophilum (Soderstr.) S. Denham, Paspalum auricomum (A. G. Burm.) S. Denham, Paspalum campylostachyum (Hack.) S. Denham, Paspalum carajasense S. Denham, Paspalum crucense (Killeen) S. Denham, Paspalum cultratum (Trin.) S. Denham, Paspalum calliferum S. Denham, Paspalum foliiforme S. Denham, Paspalum glaziovii (A. G. Burm.) S. Denham, Paspalum graniticum (A. G. Burm.) S. Denham, Paspalum huberi S. Denham, Paspalum mosquitiense (Davidse & A. G. Burm.) S. Denham, Paspalum oreophilum (A. G. Burm.) S. Denham, Paspalum orinocense S. Denham, Paspalum parrulum (A. G. Burm.) S. Denham, Paspalum procerum S. Denham, Paspalum schumannii (Pilg.) S. Denham, Paspalum seminudum (A. G. Burm.) S. Denham, Paspalum setosum (Swallen) S. Denham, Paspalum thrasyoides (Trin.) S. Denham, and Paspalum trinitense (Mez) S. Denham. Paspalum subg. Harpostachys is established to include the species previously treated in the informal Decumbentes group and in Thrasya. Paspalum subg. Harpostachys comprises 39 species that are found in the American tropics and subtropics, from the United States to Argentina and Uruguay. A key to the subgenera of Paspalum is given. The morphological and anatomical characters of subgenus Harpostachys are defined, the geographic distribution of the species is determined, and a key to differentiate the species is included. Descriptions, updated synonymy, figures, photographs, and distribution maps are provided here. Five taxa are newly synonymized: Paspalum culiacanum Vasey [= Paspalum adoperiens (E. Fourn.) Chase], Paspalum langei (E. Fourn.) Nash, Paspalum palmeri Chase [= Paspalum botterii (E. Fourn.) Chase], Thrasya reticulata Swallen [= Paspalum cinerascens (Doll) A. G. Burm. & C. N. Bastos], and Thrasya petrosa (Trin.) Chase var. ciliata A. G. Burm. [= Paspalum foliiforme S. Denham]. Finally, the geographical distribution of P. cinerascens, P. subfalcatum, P. inconstans, P. calliferum, P. huberi, P. glaziovii, and P. thrasyoides is extended.