Phylogenetic relationships in subtribe Poinae (Poaceae, Poeae) based on nuclear ITS and plastid trnT-trnL-trnf sequences^

The worldwide temperate subtribe Poinae comprises the largest grass genus, Poa (500+ species), and multiple additional small genera. We explore generic boundaries and relationships among genera of Poinae using nuclear ribosomal internal transcribed spacer data (ITS) and plastid trnT-trnh-trtiF (TLF) sequence data. ITS and TLF analyses are mostly congruent with regards to circumscription of genera, and with respect to relationships among Poinae genera, but tree structure is generally better supported among genera in the ITS strict consensus tree. ITS and TLF both support two main Poinae lineages: (;') Poa and (//) a clade comprising all other sampled Poinae. Nine small genera were nested within the large Poa clade, including Aphanelytrum, Dissanthelium, and Tovarochloa, supporting inclusion of these as sections within Poa. In the second clade, three subclades support close relationships among Nicoraepoa, Hookerochloa, and Arctagrostis; Arctophila and Dupontia; and Apera, Bellardiochloa, and Ventenata. Genera of the related subtribes Alopecurinae, Cinninae, and Miliinae were mixed among or in part external to Poinae in different ways in ITS and TLF analyses, and only subtribe Puccinelliinae was strongly supported and monophyletic. ITS analyses supported placement of Catabrosella, Hyalopoa, and Paracolpodium in Puccinelliinae (no TLF data available). The position of Poa subgenus Arctopoa is incongruent between the two analyses: TLF data support inclusion within Poa and ITS data place it outside of Poa. Similarly, TLF data resolves the genus Aniselytron outside of Poa, whereas ITS data place it within Poa. Based on these results and a consideration of morphology, we recognize Arctopoa and Aniselytron as genera, probably of ancient hybrid origins. Nothogenus xDuarctopoa is coined for Arctopoa x Dupontia, with a single nothospecies xDuarctopoa labradorica. A new combination is provided for Poa subg. Sylvestres.