On polyphyly of the former section Ochlopoa Asch. et Graebn. and hybridogenic section Acroleucae Tzvelev et Prob. (Poa L., Poaceae): insights from the molecular phylogenetic analysis

25 December 2018

Nosov, Nikolai; Tikhomirov, Valery; Machs, Eduard; Rodionov, Alexander

In this study, sequence data of the nuclear region ITS1-5.8S rDNA-ITS2 and the chloroplast region trnL-F as well as few morphological characters were examined trying to elucidate the relationships among known annual bluegrasses. It was shown that all taxa from the aggregate P. annua distinguished by lemma characters and growth form are identical according to ITS and trnL-trnF data wherein all ITS sequences of P. annua aggr. are the same as P. supina and all trnL-trnF sequences are homologous with those of P. infirma. Also we haven’t found any differences between unusual samples of P. supina with short spinules on their panicle branches and typical plants according to the sequence data though Siberian samples have minor distinction in trnL-trnF region. Our analysis showed hybrid origin of Asian annual bluegrasses (see also Nosov et al. 2015, Soreng et al. 2017). Their maternal genome is close to the section Homalopoa, but their ITS sequences were different. ITS sequences of some annual Asian bluegrasses group with the section Stenopoa and for other species (close to previous from the morphological traits) they fall into clade with the section Malacanthae. The latter group is distant from the sect. Ochlopoa and is better to be treated as a separate section, Acroleucae. American annual bluegrasses are heterogeneous and also rather distant from the sect. Ochlopoa. P. chapmaniana, species with cleistogamic flowers, is nested with basal Subantarctic sections falling out of its previously described affinity group. It is closer to the sect. Ochlopoa than other annual American bluegrasses. Thus, studied annual species in fact belong to the four independent evolutionary lines (or six including genus Eremopoa and Turkish Poa jubata – Cabi et al. 2017) one of which, Acroleucae, also passed triple reticulation event. As in previous studies our analysis didn’t support the generic status of sect. Ochlopoa.