Burke: Poa arida vs. Poa trivialis

	Poa arida	Poa trivialis
		rough-stalk blue grass
Habit		Perennial, short-lived; loosely to densely tufted, usually weakly stoloniferous.
Leaves		Basal branching intra-vaginal; culms 25-120 cm, decumbent to erect, sometimes trailing and rooting at nodes, terete or weakly compressed; nodes terete or slightly compressed, 1-3 exserted; sheaths closed for 1/3 to 1/2 of length, compressed, often densely scabrous, bases of basal sheaths glabrous, distal sheath lengths 0.5-4 times blade lengths; collars smooth or scabrous, glabrous; ligules 3-10 mm, scabrous, acute to acuminate; blades 1-5 mm wide, flat, lax, soft, sparsely scabrous over the veins, margins scabrous, apices narrowly bow-shaped.
Flowers		Spikelets 2.3-3.5 mm, lengths 3 times widths, laterally compressed; florets 2-4, bisexual; rachilla internodes smooth or muriculate; glumes distinctly keeled, keels scabrous; lower glumes subulate to narrowly lanceolate, curved, 1-veined, distinctly shorter than the lowest lemmas; calluses webbed, hirsute, hairs over 2/3 the lemma length; lemmas 2.3-3.5 mm, lanceolate, distinctly keeled, keels usually sparsely puberulent along 3/5 of length, marginal veins usually glabrous, infrequently the proximal 1/4 softly puberulent, intercostal regions smooth, glabrous, upper lemmas sometimes glabrous, lateral veins prominent, margins glabrous, apices acute; palea keels smooth, muriculate, tuberculate, or minutely scabrous; anthers 1.3-2 mm.
Fruit		Caryopses 1-4 mm, ellipsoid, usually shallowly ventrally grooved, solid; hilum sub-basal, round or oval, to 1/6 length of the caryopses.

	Poa arida	Poa trivialis
Flowering time		May-July
Habitat		Moist deciduous forest, riparian areas, disturbed grassland, and lawns at low to middle elevations.
Distribution	[WildflowerSearch map] [BONAP county map]	Occurring chiefly west of the Cascades crest in Washington; Alaska to California, east to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]
Origin		Introduced from Europe
Conservation status		Not of concern
Sibling taxa	P. alpina, P. annua, P. arctica, P. bolanderi, P. bulbosa, P. compressa, P. confinis, P. curtifolia, P. cusickii, P. fendleriana, P. glauca, P. howellii, P. infirma, P. interior, P. laxiflora, P. leibergii, P. leptocoma, P. lettermanii, P. macrantha, P. marcida, P. ×multnomae, P. nemoralis, P. nervosa, P. palustris, P. paucispicula, P. pratensis, P. secunda, P. stenantha, P. suksdorfii, P. trivialis, P. unilateralis, P. wheeleri	P. alpina, P. annua, P. arctica, P. bolanderi, P. bulbosa, P. compressa, P. confinis, P. curtifolia, P. cusickii, P. fendleriana, P. glauca, P. howellii, P. infirma, P. interior, P. laxiflora, P. leibergii, P. leptocoma, P. lettermanii, P. macrantha, P. marcida, P. ×multnomae, P. nemoralis, P. nervosa, P. palustris, P. paucispicula, P. pratensis, P. secunda, P. stenantha, P. suksdorfii, P. unilateralis, P. wheeleri
Subordinate taxa		P. trivialis ssp. trivialis
Web links	Local Web sites: Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Poa arida

Poa trivialis

rough-stalk blue grass

Habit

Perennial, short-lived; loosely to densely tufted, usually weakly stoloniferous.

Leaves

Basal branching intra-vaginal; culms 25-120 cm, decumbent to erect, sometimes trailing and rooting at nodes, terete or weakly compressed;

nodes terete or slightly compressed, 1-3 exserted;

sheaths closed for 1/3 to 1/2 of length, compressed, often densely scabrous, bases of basal sheaths glabrous, distal sheath lengths 0.5-4 times blade lengths;

collars smooth or scabrous, glabrous;

ligules 3-10 mm, scabrous, acute to acuminate;

blades 1-5 mm wide, flat, lax, soft, sparsely scabrous over the veins, margins scabrous, apices narrowly bow-shaped.

Flowers

Spikelets 2.3-3.5 mm, lengths 3 times widths, laterally compressed;

florets 2-4, bisexual;

rachilla internodes smooth or muriculate;

glumes distinctly keeled, keels scabrous;

lower glumes subulate to narrowly lanceolate, curved, 1-veined, distinctly shorter than the lowest lemmas;

calluses webbed, hirsute, hairs over 2/3 the lemma length;

lemmas 2.3-3.5 mm, lanceolate, distinctly keeled, keels usually sparsely puberulent along 3/5 of length, marginal veins usually glabrous, infrequently the proximal 1/4 softly puberulent, intercostal regions smooth, glabrous, upper lemmas sometimes glabrous, lateral veins prominent, margins glabrous, apices acute;

palea keels smooth, muriculate, tuberculate, or minutely scabrous;

anthers 1.3-2 mm.

Fruit

Caryopses 1-4 mm, ellipsoid, usually shallowly ventrally grooved, solid;

hilum sub-basal, round or oval, to 1/6 length of the caryopses.