Phylogeny of Poa (Poaceae) Based on trnT–trnF Sequence Data: Major Clades and Basal Relationships

Abstract

Poa, the largest genus of grasses (Poaceae) with over 500 species, occurs throughout temperate and boreal regions in both hemispheres. A phylogenetic study of Poa based on trnT-trnF chloroplast DNA sequence data is presented focusing on basal relationships, major clades, generic boundaries, and placement of putatively closely related genera. Results support the monophyly of the main lineage of Poa if subgen. Andinae is excluded and Anthochloa, Austrofestuca, Dissanthelium (at least in part), and Eremopoa are included. The main Poa clade and subgen. Andinae resolve within a strongly supported Poinae-Alopecurinae-Miliinae clade (PAM). The subdivision of Poa into five major clades, proposed based on chloroplast restriction site data, is supported by sequence data. The basal-most clade (ArcSyl) comprises Poa subgen. Arctopoa and subgen. Poa sect. Sylvestres, two groups having disparate morphology, but similar cpDNA. The next-diverging clade (BAPO), comprising sects. Bolbophorum, Alpinae, Parodiochloa, and Ochlopoa, is strongly supported and characterized by highly divergent cpDNA. The majority of Poa species and sections form a strongly supported clade comprising major clades SPOSTA, PoM, and HAMBADD. Newly reported in this study is Eremopoa as a distinct lineage positioned between this higher Poa clade and BAPO. A revised infrageneric classification of Poa comprising five subgenera is proposed. Two new subgeneric divisions of Poa are proposed: subgen. Stenopoa for the SPOSTA clade and supersect. Homalopoa for the HAMBADD clade. The monotypic genus Anthochloa is reduced to Poa sect. Anthochloa, and its one species recognized as Poa lepidula.

Taxonomy of Poa jubata and a new section of the genus (Poaceae)

“…The clade of J, S, V, and A is sister to R with moderate support (BS 67, pp 0.97). Soreng et al (2010) presented a simple scheme for naming ten consistently detected well-supported clades resolved within Poa in molecular phylogenetic studies (e.g., Gillespie et al, 2007Gillespie et al, , 2009). These clades often have minimal internal variation among the species and among the sections applied to the species within those clades.…”

“…Fortytwo species of Poa, including two samples of P. jubata and two subspecies of P. trivialis, were chosen to represent all subgenera of Poa (classification following Gillespie et al, 2007;Soreng et al, 2009Soreng et al, , 2010Soreng et al, , 2015aRefulio et al, 2012;Peterson and Soreng, 2016). The Poa species included in our study represent selections from all 10 plastid and 11 nrDNA genotype groups previously identified , including the x-clade .…”

Saxipoa and Sylvipoa - two new genera and a new classification for Australian Poa (Poaceae: Poinae)

“…Enlarging on our previous DNA sample of Poa species from Australia (see Introduction), we now have molecular sequence data for 26 species of Poa from Australia (18 of Australopoa), 21 species from New Zealand (5 of Australopoa) and fairly deep sampling in the genus Poa and related genera from around the World (Gillespie and Soreng 2005;Gillespie et al 2007Gillespie et al , 2009; R. J. Soreng, L. J. Gillespie, unpubl.…”

“…Considerations of morphological characteristics Jacobs et al 2008), along with plastid and nrDNA phylogenetic hypotheses (Gillespie and Soreng 2005;Gillespie et al 2007, have lead us to treat several genera within Poa (e.g. Anthochloa Nees & Meyen, Austrofestuca s.s., Eremopoa Roshev., Neuropoa, Parodiochloa C.E.Hubb., and Tzvelevia E.B.Alexeev), and exclude a few elements from it (e.g.…”

“…Druce, P. porphyroclados Nees, P. sieberiana Spreng.) were informally discussed as group 'Australopoa', a name used to cover the majority of Australian Poa (Soreng 1990;Gillespie and Soreng 2005;Gillespie et al 2007. P. drummondiana Nees of P. sect.…”