OregonFlora: Poa cuspidata vs. Poa laxiflora

	Poa cuspidata	Poa laxiflora
		looseflower bluegrass
Habit		Plants perennial, 50–120 cm; loosely cespitose or with solitary shoots, long-rhizomatous.
Culms		retrorsely scabrous.
Basal branching		extravaginal.
Leaves		sheaths closed 25–50% of their length, retrorsely scabrous; ligules 2–3.5 mm; blades flat, 3–8 mm wide.
Inflorescences		open; sparse, 14–30 cm; branches widely spreading, fairly straight; (5.5)8–12(15)cm, 1–3(4) per node, antrorsely scabrous, with 3–13 spikelets.
Spikelets		4–8 mm; florets 2–4; rachilla internodes about 1 mm long.
Glumes		keels scabrous; lower glumes lanceolate, 3-veined but margins tending to roll up, often concealing the marginal veins and appearing 1-veined; upper glumes shorter than or subequal to the lowest lemma.
Calluses		with cobwebby hairs.
Lemmas		lanceolate, 3.2–6 mm, distinctly keeled; smooth or sparsely finely scabrous; keels longvillous to 67–75% of their length; marginal vein hairs sparse, intermediate veins usually glabrous, rarely sparsely puberulent, glabrous between the veins; tips acute.
Anthers		0.5–1.1 mm.

	Poa cuspidata	Poa laxiflora
Distribution	[WildflowerSearch map] [BONAP county map]	[BONAP county map]
Discussion		Moist, shady, riparian terraces in conifer forests. 0–1100m. Casc, CR, Est, WV. WA; north to AK. Native. Poa laxiflora has an extremely open panicle with spreading, nodding branches. In P. marcida, the entire inflorescence nods, but the branches parallel the inflorescence axis, and the lemmas taper more gradually. Poa nervosa has shorter panicles, usually glabrous calluses, and longer anthers. Poa leptocoma, usually found at higher, more eastern sites, has one-veined lower glumes and a more erect inflorescence.
Source		Flora of Oregon, volume 1, page 458 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting
Sibling taxa	P. alpina, P. annua, P. bolanderi, P. bulbosa, P. chambersii, P. compressa, P. confinis, P. cusickii, P. fendleriana, P. glauca, P. howellii, P. iconia, P. infirma, P. laxiflora, P. leibergii, P. leptocoma, P. lettermanii, P. macrantha, P. mansfieldii, P. marcida, P. nemoralis, P. nervosa, P. palustris, P. piperi, P. pratensis, P. pringlei, P. reflexa, P. rhizomata, P. secunda, P. stenantha, P. suksdorfii, P. trivialis, P. unilateralis, P. wallowensis, P. wheeleri	P. alpina, P. annua, P. bolanderi, P. bulbosa, P. chambersii, P. compressa, P. confinis, P. cusickii, P. fendleriana, P. glauca, P. howellii, P. iconia, P. infirma, P. leibergii, P. leptocoma, P. lettermanii, P. macrantha, P. mansfieldii, P. marcida, P. nemoralis, P. nervosa, P. palustris, P. piperi, P. pratensis, P. pringlei, P. reflexa, P. rhizomata, P. secunda, P. stenantha, P. suksdorfii, P. trivialis, P. unilateralis, P. wallowensis, P. wheeleri
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, OR, WA 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

Poa cuspidata

Poa laxiflora

looseflower bluegrass

Habit

Plants perennial, 50–120 cm; loosely cespitose or with solitary shoots, long-rhizomatous.

Culms

retrorsely scabrous.

Basal branching

extravaginal.

Leaves

sheaths closed 25–50% of their length, retrorsely scabrous;

ligules 2–3.5 mm;

blades flat, 3–8 mm wide.

Inflorescences

open; sparse, 14–30 cm;

branches widely spreading, fairly straight; (5.5)8–12(15)cm, 1–3(4) per node, antrorsely scabrous, with 3–13 spikelets.

Spikelets

4–8 mm;

florets 2–4;

rachilla internodes about 1 mm long.

Glumes

keels scabrous;

lower glumes lanceolate, 3-veined but margins tending to roll up, often concealing the marginal veins and appearing 1-veined;

upper glumes shorter than or subequal to the lowest lemma.

Calluses

with cobwebby hairs.

Lemmas

lanceolate, 3.2–6 mm, distinctly keeled; smooth or sparsely finely scabrous;

keels longvillous to 67–75% of their length; marginal vein hairs sparse, intermediate veins usually glabrous, rarely sparsely puberulent, glabrous between the veins;

tips acute.

Anthers

0.5–1.1 mm.

Poa cuspidata

Poa laxiflora

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Moist, shady, riparian terraces in conifer forests. 0–1100m. Casc, CR, Est, WV. WA; north to AK. Native.

Poa laxiflora has an extremely open panicle with spreading, nodding branches. In P. marcida, the entire inflorescence nods, but the branches parallel the inflorescence axis, and the lemmas taper more gradually. Poa nervosa has shorter panicles, usually glabrous calluses, and longer anthers. Poa leptocoma, usually found at higher, more eastern sites, has one-veined lower glumes and a more erect inflorescence.

Source

Flora of Oregon, volume 1, page 458
Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting

Sibling taxa