Molecular phylogenetics and micromorphology of Australasian Stipeae (Poaceae), and the interrelation of whole-genome duplication and evolutionary radiations in this grass tribe

Abstract

ABSTRACTThe mainly Australian grass genusAustrostipawith ca. 64 species represents a remarkable example of an evolutionary radiation. To investigate aspects of diversification, macro- and micromorphological variation in this genus we conducted a molecular phylogenetic and scanning electron microscopy (SEM) analysis including representatives from all of its accepted subgenera.Plastid DNA variation withinAustrostipawas low and only few lineages were resolved. Nuclear ITS andAcc1yielded comparable groupings of taxa and resolved subgeneraArbuscula,Petaurista,Bambusinain a common clade and as monophyletic. In summary, we suggest recognizing nine subgenera inAustrostipa.Because of its taxonomic significance in Stipeae, we studied the lemma epidermal structure in 34 representatives ofAustrostipa.In most species, the lemma epidermal pattern (LEP) was relatively uniform (maize-like LEP), but in six species it was more similar to that ofStipas.str.,Neotrinia,PtilagrostisandOrthoraphium.The species representing subgeneraLobatae,Petaurista,BambusinaandA. muellerifrom subg.Tuberculataewere well-separated from all the other species included in the analysis.Two different sequence copies ofAcc1were found in polyploidAustrostipaandAnemanthele. Each of the copy types formed a single clade. This was also true of the sampled species ofStipas.str., but their clades were strongly separated from those ofAustrostipaandAnemanthele. This underlines the statement of Tzvelev (1977) that most if not all contemporary Stipeae are of hybrid origin and demonstrates it for the first time unambiguously on the molecular level.Chromosome number variation is surveyed and reviewed for the whole tribe Stipeae and interpreted in a molecular phylogenetic framework. The rather coherent picture of chromosome number variation underlines the phylogenetic and evolutionary significance of this character.The closest extant relatives ofAustrostipaandAnemantheleare in the clade ofAchnatherums.str.,Celtica,OloptumandStipellula. These genera are most abundant in Central and Eastern Asia, which makes a colonization of Australian and New Zealand from this region more likely, perhaps via long-distance dispersal, than colonization of Australia from southern South America via Antarctica as previously invoked.Supporting Informationmay be found online in the Supporting Information section at the end of the article.