Poa compressa L., Sp. Pl. 1: 69. 1753.

Soreng, Robert J. & Peterson, Paul M., 2012, Revision of Poa L. (Poaceae, Pooideae, Poeae, Poinae) in Mexico: new records, re-evaluation of P. ruprechtii, and two new species, P. palmeri and P. wendtii, PhytoKeys 15, pp. 1-104 : 22-23

7. Poa compressa L., Sp. Pl. 1: 69. 1753. Fig. 1 F-M

Type:

Habitat in Europae and Americae septentrionalis, (lectotype: LINN-87.41!, designated by Soreng 2000: 255).

Description.

Hermaphroditic. Perennials; extensively rhizomatous, shoots solitary, green or bluish-grey-green; tillers extravaginal (basally cataphyllous), with lateral and downward tending, cataphyllous shoots. Culms 15-60 cm tall, erect, bases usually geniculate, wiry, leafy, strongly compressed, smooth; nodes strongly compressed, 3-4 nodes usually exerted. Leaf sheaths distinctly compressed, minutely rough; butt sheaths papery, smooth, glabrous; flag leaf sheaths ca. 2-6 cm long, margins fused 10-20% the length, subequal to its blade; throats and collars smooth or slightly scabrous, glabrous; ligules 1-3 mm long, abaxially moderately to densely scabrous, upper margin ciliolate, apices obtuse; blades 1.5-4 mm wide, flat or folded, abaxially smooth, veins slightly expressed, margins scabrous, adaxially lightly scabrous over the veins, apices abruptly prow-tipped; cauline blades subequal; sterile shoot blades like those of the culm. Panicles 2-10 cm long, generally 1/6-1/3 as broad as long, erect, contracted or slightly open, linear, lanceoloid to ovoid, often interrupted, sparse to congested, with 15 to 80 spikelets; rachis with mostly 1-3 branches per node; primary branches erect to ascending, or infrequently spreading, fairly strict, 2-3 angled, angles distinctly scabrous (at least in part); lateral pedicels 1/5-2/3 their spikelet in length, scabrous, prickles moderately coarse; longest branches 0.5-3 cm, with 1-15 spikelets. Spikelets (2.3-)3.5-7 mm long, laterally compressed; not bulbiferous; grayish, often anthocyanic tinged, not lustrous; florets 3-7, hermaphroditic; rachilla internodes terete, mostly less than 1 mm long, smooth to muriculate; glumes lanceolate, subequal, distinctly keeled, keels scabrous; apices acute; lower glumes ca. 2 mm long, 3-veined; upper glumes ca. 2.1 mm long, 3-veined; calluses glabrous or more often webbed; web distinct, hairs short, woolly, sparse; lemmas 2.3-3.5 mm long, lanceolate, distinctly keeled, keels and marginal veins short villous proximally, between veins smooth, glabrous, intermediate veins obscure, margins narrowly scarious-hyaline, edges smooth or with sparsely scaberulous, apices obtuse to acute; paleas densely scabrous over the keels, between keels smooth. Flowers chasmogamous; lodicules ca. 0.6 mm long, lanceolate, with a subequal lateral lobe in the upper 2/3; anthers 1.3-1.8 mm long. Caryopses 1.4-1.5 mm long, elliptical in side-view, subtrigonous to subcylindrical in cross-section, brown, shallowly sulcate, hilum 0.2 mm long, oval, grain adherent to the palea. 2 n = 35, 42, 49, 50, 56.

Distribution.

This species is circumboreal in distribution and in North America it occurs in Canada, USA, and Mexico (Coahuila).

Ecology.

This strongly rhizomatous, ruderal species occurs in mesic, cool temperate, semi-shaded to open habitats in seasonally soggy soils, sands to clays, both derived from calcareous and igneous substrates. Once established, this species readily spreads by rhizomes.

Specimens examined.

Mexico. Coahuila: 51.6 km SE of Saltillo and 13 km SE of Jamé on road to Sierra La Viga, 3240 m, 26 Sep 1990, P.M.Peterson 10045, C.R.Annable & J.Valdes-Reyna (US).

Discussion.

This species has been introduced into the New World for soil stabilization and it is presumed also to be native in northern USA and southern Canada ( Beal 1896), but has only recently been collected in Mexico. Poa compressa is presumed to be an introduction in Mexico, although the second author has observed this species in other northern Mexico states but did not obtain vouchers because it was not flowering.

Figures

Figure 1. A-E Poa alpina L. A basal tuft B inflorescence C spikelet D floret dorsal view E floret lateral view; F-M Poa compressa L. F habit G inflorescence H culm cross-section outline I sheath, collar, blade abaxial view J branch segment with spikelet K spikelet L floret M anthers. A-M from Soreng (2007) E originally drawn from Eggleston 11824 in Hitchcock (1935).