Systematics and evolution of the needle grasses (Poaceae: Pooideae: Stipeae) based on analysis of multiple chloroplast loci, ITS, and lemma micromorphology

We conducted a molecular phylogenetic study of the tribe Stipeae using nine plastid DNA sequences (trnK-matK, matK, trnH-psbA, trnL-F, rps3, ndhF, rpl32-trnL, rpsI6-trnK, rps16 intron), the nuclear ITS DNA regions, and micromorphological characters from the lemma surface. Our large original dataset includes 156 accessions representing 139 species of Stipeae representing all genera currently placed in the tribe. The maximum likelihood and Bayesian analyses of DNA sequences provide strong support for the monophyly of Stipeae; including, in phylogenetic order, Macrochloa as remote sister lineage to all other Stipeae, then a primary stepwise divergence of three deep lineages with a saw-like (SL) lemma epidermal pattern (a plesiomorphic state). The next split is between a lineage (SL I) which bifurcates into separate Eurasian and American clades, and a lineage of three parts; a small Patis (SL2) clade, as sister to Piptathertun s.str. (SL3), and the achnatheroid clade (AC). The AC exhibits a maize-like lemma epidermal pattern throughout. AC consists of a core clade of Austral-Eurasian distribution and a major American clade of North and South American distribution. The base chromosome number for Stipeae is somewhat ambiguous but based on our survey it seems most likely to be x = 1 or 12. Our phylogenetic hypothesis supports the recognition of the following genera and groups (listed by region): Eurasia-Achnatherum,Miliacea group, Neotrinia (monotypic), Orthoraphium (monotypic), Patis (also 1 from North America), Piptatherum s.str., Psammochloa (monotypic), Ptilagrostis, Stipa, Timouria group, and Thikeraia; Mediterranean-Ampelodesmos (monotypic), Celtica (monotypic), Macrochloa (monotypic), and Stipella-Inaequiglumes group; Australasia-Anemanthele (monotypic), and Austrostipa; North America (NA)-Eriocoma group, Hesperostipa, Oryzopsis (monotypic), Piptatheropsis, Pseudoeriocoma group, and Stillmania (monotypic); South America-Aciachne, Amelichloa (also NA), Anatherostipa (s.str.), Jarava (polyphyletic), Lorenzochloa, Nassella (also NA), Ortachne, Pappostipa (also NA), and Piptochaetium (also NA). Monophyly of Phaenospermateae including Duthieinae is demonstrated, and its inclusion within or treatment as sister to Stipeae is rejected.