Phylogeny and taxonomy of the polyploidy species that contains St genome (Triticeae; Poaceae) based on four nuclear DNA and three chloroplast genes

Background The genus Pseudoroegneria (Nevski) Á. Löve with the St genome accounts for more than 60% of perennial Triticeae speciation. However, the strong dominant character of the St genome results in challenging to distinguish each species even genus based on single or combined morphological traits, the phylogeny and taxonomy of the St-containing polyploid genera remain under controversy. Results In this study, we used nuclear and chloroplast DNA-based phylogenetic analyses to reveal the systematic relationships of the St-containing polyploidy species. The maximum likelihood (ML) tree based on nuclear ribosomal internal transcribed spacer region (nrITS) and three single-copy nuclear genes data ( Acc1  +  Pgk1  +  DMC1 ) showed that St-containing polyploid species were separated into StStHH, StStYY, StStYYHH, StStYYPP, StStYYWW, StStPP, and StStEE genome types and polyploidy species in Caucasus, America and Australia have unique polyploidization events. The ML tree for the chloroplast DNA fragments ( mat K +  rbc L +  trn L- trn F) displayed that the P genome serves as a maternal donor of Kengyilia melanthera and K. dingqinensis from the Hengduan Mountains region, while the St or StY genome serves as the maternal donor of other St genome containing species. Herein, we reported the genome constitution of Kengyilia tibetica , K. changduensis , and K. dingqinensis with the StStYYPP genome for the first time. Conclusions The St-containing polyploid species should be treated as distinct genera according to different genome constitutions, St-containing polyploid species experienced independent allopolyploidization events in different distribution regions and the St-containing polyploid species had two relatively independent maternal origins from the P genome or St/StYgenome. Besides, the Xp genome may have contributed to the unknown Y genome formation.