Molecular phylogeny of Panicum s. str. (Poaceae, Panicoideae, Paniceae) and insights into its biogeography and evolution

ZULOAGA, FERNANDO OMAR; SALARIATO, DIEGO LEONEL; SCATAGLINI, AMALIA

PLOS ONE

PUBLIC LIBRARY SCIENCE

Año: 2018 vol. 13 p. 1 - 39

1932-6203

Panicumsensu stricto is a genus of grasses (Poaceae) with nearly, according tothis study, 163 species distributed worldwide. This genus is included in the subtribe Panicinae together with Louisiella, the latter with2 species. Panicum and subtribePanicinae  are characterized by includingannual or perennial taxa with open and lax panicles, and spikelets with thelower glume reduced; all taxa also share a basic chromosome number of x = 9 and a Kranz leaf blade anatomytypical of the NAD-me subtype photosynthetic pathway. Nevertheless, thephylogenetic placements of many Panicum species, and the circumscription of thegenus, remained untested. Therefore, phylogenetic analyses were conducted usingsequence data from the ndhF plastidregion, in an extensive worldwide sampling of Panicum and related genera, in order to infer evolutionaryrelationships and to provide a phylogenetic framework to review theclassification of the genus. Diversification times, historical biogeography andevolutionary patterns of the life history (annual vs. perennial) in thesubtribe and Panicum were alsostudied. Results obtained provide strong support for a monophyletic Panicum including 71 species and 7sections, of which sections Arthragrostisand Yakirra are new in the genus;7 new combinations are made here. Furthermore, 32 species traditionallyassigned to Panicum were excludedfrom the genus, and discussed in other subtribes of Paniceae. Our studysuggested that early diversification in subtribe Panicinae and Panicum occurred through the Early-MidMiocene in the Neotropics, while the subsequent diversification of its sectionsmainly occurred in the Late Miocene-Pleistocene, involving multiple dispersals toall continents. Our analyses also showed that transition rates and changesbetween annual and perennial life history in Panicum were quite frequent, suggesting considerable lability ofthis trait. Changes of the life history, together with C4photosynthesis, and the multiple dispersal events since the Mid Miocene, seemto have facilitated a widespread distribution of the genus. All these findingscontribute to a better understanding of the systematics and evolution of Panicum.