OregonFlora: Poa pratensis vs. Poa confinis

	Poa pratensis	Poa confinis
	Kentucky bluegrass	coastline 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.	slender; nodes terete, 0–1 exserted.
Basal branching	mainly extravaginal or equally extra- and intravaginal.	mainly intravaginal; some extravaginal.
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.	sheaths closed 33–50% of their length; smooth, bases of basal sheaths glabrous; collars smooth, glabrous; ligules 0.5–1.5(2.2) mm, blades of tillers with upper surface moderately to densely scabrous or very short-hairy on and between the veins; cauline blades involute, mostly filiform, 0.5–1(1.5)mm wide; lower surfaces smooth; upper surfaces sparsely scabrous on and between the veins; uppermost blade (0.5)1–5 cm long.
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.	erect; ovoid, moderately to loosely congested, 1–5(7)cm; spikelets fewer than 50; branches erect to ascending, slightly lax, 0.5–3 cm, 1–2 per node.
Spikelets		to 3 times as long as wide; compact, 3–6(8)mm; florets 2–5; rachilla internodes glabrous or sparsely softly puberulent.
Glumes		slightly unequal; keels smooth or scabrous; lower glumes 2–4 mm long, 1–3-veined; about 67% as long as the lowest lemma; upper glumes 2.9– 5 mm long.
P lants		perennial; g ynodioecious, 7–30(35)cm tall, densely to loosely tufted, rhizomatous and stoloniferous; rhizomes and stolons to 100 cm long.
Calluses		with sparse; diffuse; cobwebby hairs 1–2 mm, infrequently glabrous.
Lemmas		lanceolate, 2.5– 4(4.5)mm, distinctly keeled, moderately to densely finely scabrous, glabrous throughout or keels and sometimes marginal veins proximally sparsely softly puberulent; margins narrowly scarious; tips acute.
Anthers		vestigial and 0.1–0.2 mm or functional and 1.5–2 mm.

	Poa pratensis	Poa confinis
Distribution	[WildflowerSearch map] [BONAP county 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).	Coastal sand dunes and stabilized sandy soil, occasionally edges of coastal forests. 0–50m. Est. CA, WA; north to British Columbia. Native. 2n=42. Poa confinis is a rhizomatous grass that often puts up shoots in clusters. It grows in coastal sandy habitats. Poa macrantha grows in the same habitat but has much larger lemmas and inflorescences. Poa pratensis has long hairs on the lemma keels and marginal veins and cobwebby callus hairs that arise as a tuft on the dorsal surface, sometimes also with two additional tufts by the marginal veins.
Source	Flora of Oregon, volume 1, page 462 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 455 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. 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. 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
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 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	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 confinis

Kentucky bluegrass

coastline 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.

slender;

nodes terete, 0–1 exserted.

Basal branching

mainly extravaginal or equally extra- and intravaginal.

mainly intravaginal; some extravaginal.

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.

sheaths closed 33–50% of their length; smooth, bases of basal sheaths glabrous;

collars smooth, glabrous;

ligules 0.5–1.5(2.2) mm, blades of tillers with upper surface moderately to densely scabrous or very short-hairy on and between the veins;

cauline blades involute, mostly filiform, 0.5–1(1.5)mm wide;

lower surfaces smooth;

upper surfaces sparsely scabrous on and between the veins; uppermost blade (0.5)1–5 cm long.

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.

erect; ovoid, moderately to loosely congested, 1–5(7)cm;

spikelets fewer than 50;

branches erect to ascending, slightly lax, 0.5–3 cm, 1–2 per node.

Spikelets

to 3 times as long as wide; compact, 3–6(8)mm;

florets 2–5;

rachilla internodes glabrous or sparsely softly puberulent.

Glumes

slightly unequal;

keels smooth or scabrous;

lower glumes 2–4 mm long, 1–3-veined; about 67% as long as the lowest lemma;

upper glumes 2.9– 5 mm long.

P lants

perennial; g ynodioecious, 7–30(35)cm tall, densely to loosely tufted, rhizomatous and stoloniferous;

rhizomes and stolons to 100 cm long.

Calluses

with sparse; diffuse; cobwebby hairs 1–2 mm, infrequently glabrous.

Lemmas

lanceolate, 2.5– 4(4.5)mm, distinctly keeled, moderately to densely finely scabrous, glabrous throughout or keels and sometimes marginal veins proximally sparsely softly puberulent;

margins narrowly scarious;

tips acute.

Anthers

vestigial and 0.1–0.2 mm or functional and 1.5–2 mm.

Poa pratensis

Poa confinis

Distribution

[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).

Coastal sand dunes and stabilized sandy soil, occasionally edges of coastal forests. 0–50m. Est. CA, WA; north to British Columbia. Native. 2n=42.

Poa confinis is a rhizomatous grass that often puts up shoots in clusters. It grows in coastal sandy habitats. Poa macrantha grows in the same habitat but has much larger lemmas and inflorescences. Poa pratensis has long hairs on the lemma keels and marginal veins and cobwebby callus hairs that arise as a tuft on the dorsal surface, sometimes also with two additional tufts by the marginal veins.

Source

Flora of Oregon, volume 1, page 462
Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting

Flora of Oregon, volume 1, page 455
Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting

Sibling taxa