Phylogeny and development of Zuloagaea gen. nov. (Poaceae: Paniceae).

摘要

Classification of grasses (Poaceae) has traditionally been based on inflorescence morphology. Recent molecular investigations, however, have revealed unexpected relationships among grasses, including close relationships between species with disparate inflorescence morphologies. Such is the case with the placement of non-bristly Panicum bulbosum (sect. Bulbosa) in the "bristle clade," a monophyletic clade in the Paniceae that includes the genera Setaria, Cenchrus, and Pennisetum, among others. Here, the placement of P. bulbosum is confirmed using chloroplast markers ndhF and trnL. To investigate the morphological differences among these grasses, SEM photos detailing the development of inflorescence structures of P. bulbosum are compared with those of bristlebearing grasses and true Panicum, revealing that inflorescence development of P. bulbosum closely resembles that of the Panicum type species P. miliaceum. Cryptic bristle-like structures are seen on the inflorescence panicles of P. bulbosum late in development, and these structures may be analogous to the conspicuous bristles of the bristly grasses. To establish the number of taxa included in Panicum sect. Bulbosa, a taxomomic study is presented. Principle components analysis used on subsets of the thirty-three morphological characters assessed for the study indicate that there are no distinct morphological groups within the section. Based on molecular and morphological data, the monotypic section Bulbosa is transferred to Zuloagaea (gen. nov.), a monotypic genus including only Z. bulbosa, a montane neotropical grass.