Romaschenko, Konstantin , Peterson, Paul M. , Soreng, Robert J. .
Evolutionary history of small-spikeleted Stipeae formerly included in the Oryzopsis/Piptatherum assemblage.
The small-spikeleted Stipeae, historically considered a natural entity by Trinius (1820), Hackel (1850, 1887), Hooker (1880), Roshevitz (1951), and Freitag (1975) have small coriaceous lemmas with an obtuse callus and often short caducous awns. These species are distributed in contemporary genera: Nassella, Oryzopsis, Piptatherum, and Piptochaetium; and in formerly recognized Eriocoma that we are resurrecting. We use micro-morphological, karyological, and molecular characteristics to study these small-spikeleted Stipeae loosely referred to as the Oryzopsis/Piptatherum assemblage. Our data suggests a minimum of five independent origins of the species, and supports a much revised classification. All evidence suggests that taxa in the Oryzopsis/Piptatherum assemblage have developed similar adaptive morphological characters via convergence. We provide evidence for recognition of Oryzopsis as a monotypic North American genus nested within a set of relict Asian genera: Trikeraia, Psammochloa, and Neotrinia. We propose a new genus, Piptatheropsis, for five North American species currently placed in Piptatherum (P. shoshoneanum, P. exiguum, P.micranthum, P. canadense, and P. pungens), but previously included in Oryzopsis s.l., since they are sister to Piptochaetium and Anatherostipa. The other New World species in Piptatherum (P. racemosum) is sister to the Patis group of East Asian origin that includes Patis coreana and Piptatherum kuoi. This shows an additional biogeographical connection between New and Old World Stipeae. Our morphological and molecular data support the transfer of species of Piptatherum sect. Virescentia into Achnatherum s.s. and the removal of most of the North American Achnatherum to Eriocoma. Piptatherum s.s. is an independent Asian group containing the type P. coerulescens and at least 23 other species. The generic description of Piptatherum is emended to contain only species with dorsally compressed florets with transverse-elliptic disarticulation scars and basally open lemma borders that expose a coriaceous palea.
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1 - Botanic Institute of Barcelona, Botany, csic-icub, Pg. del Migdia, s.n., Barcelona, 08038, Spain
2 - Smithsonian, Department of Botany, National Museum of Natural History, P.O. Box 37012, Washington, DC, 20013, USA
3 - Smithsonian, Department of Botany, National Museum of Natural History, P.O. Box 37012, Washington, DC, 20013, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 556B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 10:00 AM