Taxonomy of the Poa laxa group, including two new taxa from Arctic Canada and Greenland, and Oregon, and a re‐examination of P. sect. Oreinos (Poaceae)

Abstract

The Poa laxa Haenke species group, comprising four alpine-arctic taxa in P. sect. Oreinos, has a complicated and confusing taxonomic history. Here we re-examine the taxonomy of the group and section based on sequences of three plastid and two nuclear ribosomal DNA markers. Poa laxa s.l. resolved in a clade with species of sections Abbreviatae, Oreinos, Stenopoa, and Tichopoa. In the plastid analyses, Poa laxa s.s. (type of sect. Oreinos) was placed in a subclade with P. glauca and other sect. Stenopoa species, while all other P. laxa s.l. taxa were placed in a subclade with species of sect. Abbreviatae. We maintain P. laxa s.s. (mainly 2n  28) of west-central Europe in sect. Oreinos, while the other P. laxa s.l. taxa from northern Europe and North America (all 2n  42 or higher ploid) are referred to P. sect. Abbreviatae. In North America only one collection of the northern European P. flexuosa subsp. flexuosa is accepted (Greenland, Jensen's Nunatakker), and P. flexuosa subsp. fernaldiana is accepted based on populations in eastern Canada and northeast USA. A new subspecies, P. flexuosa subsp. consauliae, is described from eastern Arctic Canada and Greenland; its variable morphological characteristics suggest introgression with P. glauca and it is predicted to be apomictic. Rocky Mountain P. laxa subsp. banffiana is treated as P. banffiana. Oregon material formerly considered to belong to P. laxa s.l. is named P. wallowensis. Poa sect. Oreinos is thus found to be polyphyletic, and is here emended to comprise only three continental European species, including P. laxa. Lectotypes are designated for P. aspera var. laxiuscula, P. fernaldiana, P. flexuosa, and P. laxa var. debilior. New chromosome numbers are reported for P. flexuosa subsp. consauliae (ca 2n  42), and P. glauca (2n  63) from Baffin Island. A key to the species and subspecies found in North America is given.

Phylogeny and taxonomic synopsis of Poa subgenus Pseudopoa (including Eremopoa and Lindbergella) (Poaceae, Poeae, Poinae)

“…Pandemos: P.trivialis L.). Poa major clades have been described elsewhere (Gillespie et al 2007, 2008, 2009, Soreng et al 2010, 2017b, Cabi et al 2017); here we focus on the position of Eremopoa .…”

“…Trees were viewed in FigTree v1.4.0 (Rambaut 2006+). Clade designations follow Soreng et al (2010) with modifications as in Cabi et al (2017) and Soreng et al (2017b), wherein well-supported major clades are assigned letters.…”

Updated checklist of Poa in the Iberian Peninsula and Balearic Islands

“…Poa because that section includes the type species; species are then ordered according to phylogenetic relationships, an arrangement more or less the inverse of that adopted by other authors, i.e. from more derived clades to those in a more basal position (see Gillespie et al 2008; Soreng et al 2010, 2017). …”

“…P. annua ) (Soreng et al 2010). The genus comprises approximately 550 annual and perennial species (Soreng et al 2017) of cosmopolitan distribution, primarily in cold and temperate regions. Most species are polyploids, but 9% are diploids, with an additional 4%–6%, mostly in Europe and rarely in Asia, having both diploid and polyploid populations (Soreng et al 2010, Giussani et al 2016).…”

Poa secunda J. Presl (Poaceae): a modern summary of infraspecific taxonomy, chromosome numbers, related species and infrageneric placement based on DNA

“…Our phylogenetic studies, based on plastid and nuclear ribosomal DNA, demonstrate that sect. Secundae is reticulate in origin (Gillespie et al 2008, Cabi et al 2017, Soreng et al 2017). Secundae species exhibit several atavistic traits (Soreng 1991a, Soreng et al 2015) that are otherwise odd in Poa , including; a crown of hairs around the base of the callus, upper culm leaf sheaths margins often free more than 80–90% of their length and lemmas that are often somewhat rounded on the back.…”