Phylogenetic structure of the grass subfamily Pooideae based on comparison of plastid matK gene-3′trnK exon and nuclear ITS sequences

The grass Subfamily Pooideae was Studied using DNA sequence information from the chloroplast (cp) matK gene-3'trnK exon and the nuclear ribosomal (nr) ITSI-5.8S gene-ITS2 in a sample of 67 taxa covering all of its tribes. Branches with strong bootstrap support are consistently resolved in both datasets, whereas discrepancy is confined to low-support or unsupported nodes in one of the datasets. The results do not reveal a significant role of past hybridisation, plastid lineage sorting or reticulation in the evolutionary diversification of the major lineages of the Subfamily. The combined analysis of the plastid and nuclear datasets results in a largely well-supported pattern of divergence for the major lineages of the Subfamily. Some re-alignments of tribes and subtribes are proposed and discussed with reference to relevant morphological and Structural characters. We propose the recognition of broader tribes Nardeae with subtribes Nardinae and Lygeinae, Meliceae with subtribes Brylkiniinae and Melicinae, Stipeae with subtribes Ampelodesminae and Stipinae, and Triticeae with subtribes Littledaleinae, Brominae and Hordeinae. For the tribe complex of Aveneae and Poeae, the clear-cut split into two major clades and further resolution into some high-support lineages depicted by cpDNA is not contradicted by nuclear ITS and their taxonomic treatment as separate tribes or a single tribe remains ail unanswered question.