Phylogenetic studies favour the unification of Pennisetum, Cenchrus and Odontelytrum (Poaceae): a nuclear, plastid and morphological combined analysis, and nomenclatural combinations in Cenchrus

M. AMELIA CHEMISQUY, LILIANA M. GIUSSANI, MARÍA A. SCATAGLINI, ELIZABETH A. KELLOGG, OSVALDO MORRONE

ANNALS OF BOTANY

OXFORD UNIV PRESS

Año: 2010 vol. 106 p. 107 - 130

0305-7364

·  Backgrounds and aims: Twenty-five genera having sterile inflorescence branches were recognized as the bristle clade within the x = 9 Paniceae (Panicoideae). Within the bristle clade, taxonomic circumscription of Cenchrus (20-25 species), Pennisetum (80-140) and the monotypic Odontelytrum is still unclear. Several criteria have been applied to characterize Cenchrus and Pennisetum, but none of these has been satisfactory since the diagnostic characters, such as fusion of bristles in the inflorescences, present continuous variation. ·  Methods: We present a phylogenetic analysis based on morphological, plastid (trnL-F, ndhF) and nuclear (knotted) data for a representative species sampling of the genera. All analyses were conducted under parsimony, using heuristic searches with TBR branch swapping. Branch support was assessed with parsimony jackknifing. ·  Key results: Based on plastid and morphological data, Pennisetum, Cenchrus and Odontelytrum were supported as a monophyletic group: the PCO clade. Only one section of Pennisetum (Brevivalvula) was supported as monophyletic. The position of P. lanatum differed among data partitions, although the combined plastid and morphology and nuclear analyses found this species to be included in the PCO clade. The basic chromosome number x = 9 was found to be plesiomorphic, and x = 5, 7, 8, 10 and 17 were derived states. The nuclear phylogenetic analysis revealed a reticulate pattern of relationships among Pennisetum and Cenchrus, suggesting that there are at least three different genomes. Because apomixis can be transferred among species through hybridization, its history most likely reflects crossing relationships, rather than multiple independent appearances. ·  Conclusions: Due to the consistency between our results and different phylogenetic hypotheses (including morphological, developmental and multilocus approaches), and the high support found for the PCO clade, also including the type species of the three genera, we propose unification of Pennisetum, Cenchrus and Odontelytrum. Species of Pennisetum and Odontelytrum are here transferred into Cenchrus, which has priority. A total of 66 new combinations are listed herein.