PHYLOGENY AND CIRCUMSCRIPTION OF THE GENUS Orinus (Poaceae: Eragrostideae): EVIDENCE FROM NRDNA ITS SEQUENCES

In this study, ITS sequences of the nuclear ribosomal DNA were conducted for six putative species of Orinus (O. alticulmus, O. anomala, O. kokonorica, O. longiglumis, O. thoroldii and O. tibeticus) with 572 individuals from 73 populations. The results found that the six species formed two monophyletic groups: the one (O. anomala Keng ex Keng f. and L. Liou) with O. alticulmus, O. anomala and O. kokonorica, and another (O. thoroldii (Stapfex Hemsl.) Bor) with O. longiglumis, O. thoroldii and O. tibeticus. The taxonomic data from ITS sequences were not congruent with those from morphological characteristics, likely resulting from rapid speciation trigged by the uplifts of the Qinghai-Tibetan Plateau and its adjacent regions and the extensive selection pressure under the alpine environments. The ITS data suggest that the classification of the six species within the genus Orinus should be reduced to two species. We include a complete taxonomic revision of the genus and a key to distinguish the two species. Therefore, it is very necessary to make the comprehensive revision and arrangement of these taxa, strictly regulate the taxa confusion of genus and species order, and do new reports on belonging to the genus taxa.