Abstract
The mainly Australian grass genus Austrostipa (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 Austrostipa’s currently accepted subgenera. Because of its taxonomic significance in Stipeae, we studied the lemma epidermal pattern (LEP) in 34 representatives of Austrostipa. Plastid DNA variation within Austrostipa was low and only few lineages were resolved. Nuclear ITS and Acc1 yielded comparable groupings of taxa and resolved subgenera Arbuscula, Petaurista, and Bambusina in a common clade and as monophyletic. In most of the Austrostipa species studied, the LEP was relatively uniform (typical maize-like), but six species had a modified cellular structure. The species representing subgenera Lobatae, Petaurista, Bambusina as well as A. muelleri from subg. Tuberculatae were well-separated from all the other species included in the analysis. We suggest recognizing nine subgenera in Austrostipa (with number of species): Arbuscula (4), Aulax (2), Austrostipa (36), Bambusina (2), Falcatae (10), Lobatae (5), Longiaristatae (2), Petaurista (2) and the new subgenus Paucispiculatae (1) encompassing A. muelleri. Two paralogous sequence copies of Acc1, forming two distinct clades, were found in polyploid Austrostipa and Anemanthele. We found analogous patterns for our samples of Stipa s.str. with their Acc1 clades strongly separated from those of Austrostipa and Anemanthele. 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.
Highlights
IntroductionFeathergrasses (tribe Stipeae) have long attracted the interest of scientists because of their enormous morphological variation and because of their worldwide ecological significance as important constituents of grasslands (steppes, prairies) under mesic to xeric, sometimes in rather cold climates, where they are often an important source of food for livestock (e.g., Kellogg, 2015)
Feathergrasses have long attracted the interest of scientists because of their enormous morphological variation and because of their worldwide ecological significance as important constituents of grasslands under mesic to xeric, sometimes in rather cold climates, where they are often an important source of food for livestock (e.g., Kellogg, 2015)
By using a combination of morphological and molecular approaches, this study addresses the main phylogenetic and evolutionary problems regarding Austrostipa, namely its monophyly and its internal phylogenetic structure
Summary
Feathergrasses (tribe Stipeae) have long attracted the interest of scientists because of their enormous morphological variation and because of their worldwide ecological significance as important constituents of grasslands (steppes, prairies) under mesic to xeric, sometimes in rather cold climates, where they are often an important source of food for livestock (e.g., Kellogg, 2015). Many Austrostipa species seem to be edaphically specialized, being restricted to specific soil types (Everett et al, 2009; Williams, 2011)
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