Poa autumnalis
Poa compressa
autumn bluegrass
Canada blue grass, Canadian blue grass, flat-stem blue grass
23-86 cm tall, 0.8-1.8 mm thick, bases often decumbent.
15-60 cm, wiry, bases usually geniculate, strongly compressed;
nodes strongly compressed, some proximal nodes usually exserted.
closed for 1/3 – 1/2 their length;
ligules 0.2-1.9(2.5) mm, smooth or obtuse;
blades (0.5)1-4 mm wide, flat or folded, thin.
closed for 1/10 – 1/5 their length, distinctly compressed, bases of basal sheaths glabrous;
ligules 1-3 mm, moderately to densely scabrous, ciliolate, apices obtuse;
blades 1.5-4 mm wide, flat, cauline blades subequal.
mainly pseudointravaginal.
(5)8-20 cm, erect or lax, broadly pyramidal at maturity, open, sparse, lower axils sometimes sparsely pubescent;
nodes with 1-2(4) branches;
branches 5-12 cm, spreading to reflexed, straight, angled, angles scabrous, with 3-8 spikelets in the distal 1/4-1/3.
2-10 cm, generally 1/6 - 1/3 as wide as long, erect, linear, lanceoloid to ovoid, often interrupted, sparse to congested, with 15-80 spikelets and mostly with 1-3 branches per node;
branches 0.5-3 cm, erect to ascending, or infrequently spreading, angles densely scabrous, at least in part, with 1-15 spikelets.
3-8.2 mm, laterally compressed;
florets 2-4(6);
rachilla internodes smooth, sparsely softly puberulent.
(2.3)3.5-7 mm, laterally compressed;
florets 3-7;
rachilla internodes usually shorter than 1 mm, smooth to muriculate.
distinctly shorter than the adjacent lemmas, distinctly keeled, keels scabrous;
lower glumes subulate to lanceolate, (1)3-veined;
upper glumes lanceolate to broadly lanceolate;
calluses usually glabrous, rarely sparsely and shortly webbed;
lemmas (2.8)3-4.6 mm, lanceolate, distinctly keeled, keels and marginal veins short- to long-villous, hairs extending up 3/4 of the keel, lateral veins prominent, intercostal regions softly puberulent, smooth, apices obtuse, blunt;
palea keels softly puberulent to short-villous for much of their length, apices scabrous;
anthers 1-1.4(2.6) mm.
distinctly keeled;
lower glumes 3-veined;
calluses usually webbed, sometimes glabrous;
lemmas 2.3-3.5 mm, lanceolate, distinctly keeled, keels and marginal veins short-villous, intercostal regions glabrous, lateral veins obscure, margins glabrous, apices acute;
paleas scabrous over the keels;
anthers 1.3-1.8 mm.
= 28.
= 35, 42, 49, 50, 56, 84.
Poa autumnalis
Poa compressa
Poa autumnalis grows primarily in the southeastern United States, being found in forests of the eastern and western Appalachian piedmont and coastal plain. It is readily distinguished from other perennial species of the eastern United States by its combination of glabrous calluses and pubescent palea keels.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Poa compressa is common in much of the Flora region. It is sometimes considered to be native, but this seems doubtful. It is rare and thought to be introduced in Siberia and only local in the Russian Far East, but is common in Europe. In the Flora region, it is often seeded for soil stabilization, and has frequently escaped. It grows mainly in riparian areas, wet meadows, and disturbed ground. Its distinctly compressed nodes and culms, exserted lower culm nodes, rhizomatous growth habit, and scabrous panicle branches make it easily identifiable.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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