4 Discussion
The morphological characters of R. yenchiana differ from all species previously described in Roegneria , especially in its rudimentary spikelets at the inflorescence base, rectangular glumes, and two short mucros in lemmas. GISH conformed that R. yenchicata is a tetraploid (2n=4x=28) with the StY genome constitution. Phylogenetic analysis based on all the three unlinked single-copy sequences showed that the St -genome homoeologous types ofR. yenchiana were grouped with the sequences ofPseudoroegneria and Roegneria , and the Y -genome homoeologous types of R. yenchiana were clustered with the sequences of Roegneria with high statistic supports (BS > 70% and PP > 0.9). In the phylogenetic tree inferred from the combined chloroplast sequences, all the three accessions of R. yenchiana were grouped withPseudoroegneria and Roegneria (BS = 81% and PP = 1.0). These results indicated that Pseudoroegneria andRoegneria are closely related to R. yenchiana . Combined with GISH analysis, it can be concluded that the St genome ofR. yenchiana is derived from the genus Pseudoroegneria , and the Pseudoroegneria served as the maternal donors during its polyploid speciation.