Phylogenetic relationships among Poaceae and related families as inferred from morphology, inversions in the plastid genome, and sequence data from the mitochondrial and plastid genomes

Abstract

A phylogenetic analysis of the Poales was conducted to assess relationships among Poaceae and allied families. The analysis included 40 taxa, representing all families of the Poales as circumscribed by the Angiosperm Phylogeny Group (APG), plus five of the six unplaced Commelinid families in the APG system. The data matrix included 98 informative characters representing variation in morphology and chloroplast genome structure (including three inversions in the chloroplast genome), and 563 informative characters derived from rbcL and atpA nucleotide sequences. Ecdeiocolea has the 6-kilobase (kb) chloroplast genome inversion previously reported in Joinvillea and Poaceae, and like Joinvillea it lacks the trnT inversion that occurs in grasses. Analysis of the morphological data places Poaceae in an unresolved relationship relative to several other taxa, including Joinvillea and Ecdeiocolea, while analysis of the molecular and combined data resolves Ecdeiocolea as sister of Poaceae, with Joinvillea the sister of this group. Although the 6-kb and trnT inversions are non-homoplasious in the phylogenies obtained in this study, the 28-kb inversion is optimized as having originated twice (once in Restionaceae and another time in the most recent common ancestor of Ecdeiocolea, Joinvillea, and the grasses); an alternative interpretation is that it arose once and was later lost in Anarthria. Ecdeiocolea shares with Poaceae the presence of operculate, annulate pollen that lacks scrobiculi, and a dry, indehiscent fruit.