Molecular Phylogenetics and Micromorphology of Australasian Stipeae (Poaceae, Subfamily Pooideae), and the Interrelation of Whole-Genome Duplication and Evolutionary Radiations in This Grass Tribe

The mainly Australian grass genus (tribe Stipeae) comprising approximately 64 species represents a remarkable example of an evolutionary radiation. To investigate aspects of diversification, macro- and micromorphological variation in this genus, we conducted molecular phylogenetic and scanning electron microscopy (SEM) analyses including representatives from most of 's currently accepted subgenera. Because of its taxonomic significance in Stipeae, we studied the lemma epidermal pattern (LEP) in 34 representatives of Plastid DNA variation within was low and only few lineages were resolved. Nuclear ITS and yielded comparable groupings of taxa and resolved subgenera , , and in a common clade and as monophyletic. In most of the species studied, the LEP was relatively uniform (typical maize-like), but six species had a modified cellular structure. The species representing subgenera , , as well as from subg. were well-separated from all the other species included in the analysis. We suggest recognizing nine subgenera in (with number of species): (4), (2), (36), (2), (10), (5), (2), (2) and the new subgenus (1) encompassing . Two paralogous sequence copies of , forming two distinct clades, were found in polyploid and . We found analogous patterns for our samples of s.str. with their clades strongly separated from those of and . This underlines a previous hypothesis of Tzvelev (1977) that most extant Stipeae are of hybrid origin. We also prepared an up-to-date survey and reviewed the chromosome number variation for our molecularly studied taxa and the whole tribe Stipeae. The chromosome base number patterns as well as dysploidy and whole-genome duplication events were interpreted in a phylogenetic framework. The rather coherent picture of chromosome number variation underlines the enormous phylogenetic and evolutionary significance of this frequently ignored character.