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

CHEMISQUY M. A., GIUSSANI L.M., SCATAGLINI M.A., KELLOGG E.A., MORRONE O.

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 bristleclade within the x ¼ 9 Paniceae (Panicoideae). Within the bristle clade, taxonomic circumscription of Cenchrus(20 a 25 species), Pennisetum (80 a 140) and the monotypic Odontelytrum is still unclear. Several criteria havebeen applied to characterize Cenchrus and Pennisetum, but none of these has proved satisfactory as the diagnosticcharacters, such as fusion of bristles in the inflorescences, show continuous variation.Methods A phylogenetic analysis based on morphological, plastid (trnL-F, ndhF) and nuclear (knotted) data ispresented 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 supportedas 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 morphologyand nuclear analyses showed this species to be a member of the PCO clade. The basic chromosomenumber x ¼ 9 was found to be plesiomorphic, and x ¼ 5, 7, 8, 10 and 17 were derived states. The nuclear phylogeneticanalysis revealed a reticulate pattern of relationships among Pennisetum and Cenchrus, suggesting thatthere 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 the present results and different phylogenetic hypotheses (includingmorphological, 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 andOdontelytrum. Species of Pennisetum and Odontelytrum are here transferred into Cenchrus, which has priority.Sixty-six new combinations are made here.