Phylogenetic relationships of the genus Piptochaetium (Poaceae, Pooideae, Stipeae): Evidence from morphological data

A systematic treatment of the entire genus Piptochaetium, which complements that of Cialdella and Arriaga for the South American species, is presented herein. A synopsis of 36 species and 2 varieties, a key to identify these species as well as synonymy and geographical distribution, are given. Illustrations and photographs of diagnostic characters are presented for the North American species for the first time. We propose a phylogenetic hypothesis for the genus based on morphological and anatomical characters. Monophyly of Piptochaetium was supported by the combination of three synapomorphies: a grooved palea, involute lemma margins that fit into a longitudinal palea groove, and the palea protruding from the lemma. Two sections were previously recognized in Piptochaetium: Podopogon and Piptochaetium. The cladistic analysis showed that only South American species of Piptochaetium sect. Piptochaetium, together with P. brevicalyx, form a monophyletic group (Obovoid group), while Piptochaetium sect. Podopogon is polyphyletic. Therefore, the taxonomic recognition of sectional taxa cannot be supported. Phylogenetic relationships of two varieties of Piptochaetium stipoides (var. stipoides and var. echinulatum) were not clearly resolved. Furthermore, based on cladistic analysis, taxonomic observations, and the study of type material, Piptochaetium tovarii subsp. pilosa is raised to specific rank (= P. pilosum).