Zuloagaea, a new genus of neotropical grass within the "bristle clade" (Poaceae: Paniceae)

Recent molecular data indicate that "Panicum" section Bulbosa does not belong in the genus Panicum. Previously published phylogenies strongly support its inclusion in the "bristle clade," a monophyletic group in the Paniceae that includes the genera Setaria, Cenchrus, and Pennisetum, among others. The morphological synapomorphy for the clade is the presence of bristles (sterile branchlets) in the inflorescence, but Panicum bulbosum has no bristle-like structures at any stage of development, and is otherwise morphologically quite distinct from any of its close relatives. We have evaluated several possible taxonomic placements for section Bulbosa, reflecting the need to remove it from Panicum. Our conclusion, based on previously published molecular and current morphological data, is to erect a new genus, Zuloagaea, to accommodate section Bulbosa. We have also evaluated whether there are one, two, or three taxa within sect. Bulbosa. We have used principal components analysis of 33 morphological characters and find no distinct morphological groups within the section, and hence conclude that the group represents a single species.