OregonFlora: Poa arida vs. Poa pratensis

	Poa arida	Poa pratensis
		Kentucky bluegrass
Habit		Plants perennial, 5–70(100)cm tall, densely to loosely cespitose and extensively rhizomatous.
Culms		nodes terete or slightly compressed, 1–2(3) nodes exposed.
Basal branching		mainly extravaginal or equally extra- and intravaginal.
Leaves		sheaths closed 25–50% of their length, bases of basal sheaths glabrous; collars smooth, glabrous; ligules truncate to rounded, 0.9–2(3.1)mm, blades of extravaginal shoots like cauline blades, those of intravaginal shoots; when present, sometimes distinctly narrower; flat to involute, 0.4–1 mm wide; cauline blades flat or folded; to involute on the margins, 0.4–4.5 mm wide; lower surfaces smooth, glabrous; upper surfaces smooth or sparsely scabrous, frequently with sparse; slender hairs 0.2–0.8 mm long; uppermost blades 1.5–10 cm.
Inflorescences		narrowly ovoid to narrowly or broadly pyramidal, loosely contacted to open, sparsely to moderately congested, 2–15(20)cm; spikelets (25)30–100+; branches spreading; (1)2–9 cm long; (1)2–7(9) per node; spikelets 4–30(50), usually fairly crowded in distal half.

	Poa arida	Poa pratensis
Distribution	[WildflowerSearch map] [BONAP county map]	[WildflowerSearch map] [BONAP county map]
Discussion		6 subspecies; 5 subspecies treated in Flora. Poa pratensis is a common grass with slightly nodding inflorescences and copious cobwebby callus hairs. Poa rhizomata, of rocky ultramafic slopes in southwestern Oregon, is similar but has sparse inflorescences, acute ligules, and unisexual inflorescences. Poa confinis of coastal sands has glabrous (to sparsely hairy) lemmas and diffuse, not tufted callus hairs. Poa wheeleri, a common eastern Oregon species, lacks the lemma hairs and has denser inflorescences and more strongly scabrous leaf sheaths. Poa pratensis is common, polyploid, and highly variable. It hybridizes with related taxa including P. alpina, P. secunda, and P. wheeleri. The resulting variation in P. pratensis can be perpetuated through both sexual and asexual seed production, resulting in many recognizable forms that are linked by intermediates. Most or all Poa pratensis found in Oregon are descended from three introduced subspecies (P. p. ssp. angustifolia, P. p. ssp. pratensis, and P. p. ssp. irrigata).
Source		Flora of Oregon, volume 1, page 462 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. laxiflora, P. leibergii, P. leptocoma, P. lettermanii, P. macrantha, P. mansfieldii, P. marcida, P. nemoralis, P. nervosa, P. palustris, P. piperi, P. pringlei, P. reflexa, P. rhizomata, P. secunda, P. stenantha, P. suksdorfii, P. trivialis, P. unilateralis, P. wallowensis, P. wheeleri
Subordinate taxa		P. pratensis ssp. agassizensis, P. pratensis ssp. alpigena, P. pratensis ssp. angustifolia, P. pratensis ssp. irrigata, P. pratensis ssp. pratensis
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 arida

Poa pratensis

Kentucky bluegrass

Habit

Plants perennial, 5–70(100)cm tall, densely to loosely cespitose and extensively rhizomatous.

Culms

nodes terete or slightly compressed, 1–2(3) nodes exposed.

Basal branching

mainly extravaginal or equally extra- and intravaginal.

Leaves

sheaths closed 25–50% of their length, bases of basal sheaths glabrous;

collars smooth, glabrous;

ligules truncate to rounded, 0.9–2(3.1)mm, blades of extravaginal shoots like cauline blades, those of intravaginal shoots; when present, sometimes distinctly narrower; flat to involute, 0.4–1 mm wide;

cauline blades flat or folded; to involute on the margins, 0.4–4.5 mm wide;

lower surfaces smooth, glabrous;

upper surfaces smooth or sparsely scabrous, frequently with sparse; slender hairs 0.2–0.8 mm long; uppermost blades 1.5–10 cm.

Inflorescences

narrowly ovoid to narrowly or broadly pyramidal, loosely contacted to open, sparsely to moderately congested, 2–15(20)cm;

spikelets (25)30–100+;

branches spreading; (1)2–9 cm long; (1)2–7(9) per node;

spikelets 4–30(50), usually fairly crowded in distal half.

Poa arida

Poa pratensis

Distribution

[WildflowerSearch map]

[BONAP county map]

[WildflowerSearch map]

[BONAP county map]

Discussion

6 subspecies; 5 subspecies treated in Flora.

Poa pratensis is a common grass with slightly nodding inflorescences and copious cobwebby callus hairs. Poa rhizomata, of rocky ultramafic slopes in southwestern Oregon, is similar but has sparse inflorescences, acute ligules, and unisexual inflorescences. Poa confinis of coastal sands has glabrous (to sparsely hairy) lemmas and diffuse, not tufted callus hairs. Poa wheeleri, a common eastern Oregon species, lacks the lemma hairs and has denser inflorescences and more strongly scabrous leaf sheaths. Poa pratensis is common, polyploid, and highly variable. It hybridizes with related taxa including P. alpina, P. secunda, and P. wheeleri. The resulting variation in P. pratensis can be perpetuated through both sexual and asexual seed production, resulting in many recognizable forms that are linked by intermediates. Most or all Poa pratensis found in Oregon are descended from three introduced subspecies (P. p. ssp. angustifolia, P. p. ssp. pratensis, and P. p. ssp. irrigata).