Phylogenetics of Panicoideae (Poaceae) based on chloroplast and nuclear DNA sequences

Phylogenetic relationships among major subfamilies in Poaceae and among major tribes within Panicoideae were evaluated using parsimony and Bayesian analyses of chloroplast trnL–F and atpβ–rbcL DNA sequences and a nuclear ribosomal DNA sequence, ITS1–ITS2. The PanicoideaeAristidoideae-Chloridoideae-Micrairoideae-Arundinoideae-Danthonioideae (PACMAD) clade was well resolved. A close relationship between Aristidoideae and Chloridoideae was found. The monophyly of Micrairoideae was resolved but the relationships of three tribes (Eriachneae, Isachneae, Micraireae) within Micrairoideae were unclear, only Eriachne and Isachne were monophyletic. Panicoideae sensu stricto were supported as monophyletic and sister to a clade of Danthoniopsis and Tristachya. Within Panicoideae, only a clade of Andropogoneae + Arundinella + Garnotia was supported. None of the analyses supported the monophyletic status of Paniceae. Within Paniceae, the bristle clade (excluding Cenchrus) + Alexfloydia, and the forest shade clade sensu Giussani et al. (2001), were found, but their circumscription remains ambiguous. A sister relationship between the endemic and rare Australian grasses Homopholis and Walwhalleya was also resolved. Arundinelleae were found to be polyphyletic. This study supported the separation of Arundinella and Garnotia from the remaining Arundinelleae and the inclusion of both genera in their own subtribes (Arundinellinae Honda sensu stricto and Garnotiinae Pilger) within the Andropogoneae. Arundinelleae should be abandoned as a taxonomic tribe within the Centothecoid + Panicoid clade. Within Andropogoneae, five out of a total of 11 subtribes (Chionachninae, Coicinae, Dimeriinae, Germainiinae, and Tripsacinae) were monophyletic. This was the first time that Dimeriinae and Germainiinae have been included in a molecular study.