OregonFlora: Poa annua vs. Poa pratensis

	Poa annua	Poa pratensis
	annual bluegrass	Kentucky bluegrass
Habit	Plants annual, rarely biennial, 2–20(45)cm tall; cespitose.	Plants perennial, 5–70(100)cm tall, densely to loosely cespitose and extensively rhizomatous.
Culms	nodes terete or weakly compressed.	nodes terete or slightly compressed, 1–2(3) nodes exposed.
Basal branching	intravaginal.	mainly extravaginal or equally extra- and intravaginal.
Leaves	sheaths closed about 33% of their length; ligules 0.5–3(5) mm; blades flat or weakly folded, 1–10 cm × 1–3(6)mm; smooth.	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	1–7(10)cm; branches ascending to spreading or reflexed.	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.
Spikelets	3–5 mm long; florets 2–6; rachilla internodes smooth, glabrous; more or less concealed, occasionally exposed; distal rachilla internode less than 50(75)% of the length of distal lemma.
Glumes	lower glumes smooth, 1-veined.
Calluses	glabrous.
Lemmas	lanceolate, 2.5–4 mm, keeled; smooth; keels; marginal veins; and usually intermediate veins crisply puberulent to long-villous, rarely glabrous; area between veins glabrous; tips obtuse to acute.
Anthers	0.6–1.1 mm, oblong.
2n	=28.

	Poa annua	Poa pratensis
Distribution	[WildflowerSearch map] [BONAP county map]	[WildflowerSearch map] [BONAP county map]
Discussion	Disturbed areas, parking lots, lawns, shores. 0–1700m. BR, BW, Casc, Col, CR, Est, Lava, Sisk, WV. CA, ID, NV, WA; throughout southern Canada and US; worldwide. Exotic. Poa annua is a small but abundant annual with spreading inflorescence branches and oblong anthers. Poa infirma is very similar but has ascending inflorescence branches and shorter, nearly spherical anthers. Poa supina, supine bluegrass, has inflorescences similar to P. annua, but it is a stoloniferous perennial with longer anthers. It is planted on shady golf courses and lawns where it forms dense, spongy turf. It has not been found in the wild in Oregon but is expected to escape here.	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 453 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 462 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting
Sibling taxa	P. alpina, 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 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	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 pratensis

annual bluegrass

Kentucky bluegrass

Habit

Plants annual, rarely biennial, 2–20(45)cm tall; cespitose.

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

Culms

nodes terete or weakly compressed.

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

Basal branching

intravaginal.

mainly extravaginal or equally extra- and intravaginal.

Leaves

sheaths closed about 33% of their length;

ligules 0.5–3(5) mm;

blades flat or weakly folded, 1–10 cm × 1–3(6)mm; smooth.

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

1–7(10)cm;

branches ascending to spreading or reflexed.

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.

Spikelets

3–5 mm long;

florets 2–6;

rachilla internodes smooth, glabrous; more or less concealed, occasionally exposed;

distal rachilla internode less than 50(75)% of the length of distal lemma.

Glumes

lower glumes smooth, 1-veined.

Calluses

glabrous.

Lemmas

lanceolate, 2.5–4 mm, keeled; smooth; keels; marginal veins; and usually intermediate veins crisply puberulent to long-villous, rarely glabrous; area between veins glabrous;

tips obtuse to acute.

Anthers

0.6–1.1 mm, oblong.

=28.

Poa annua

Poa pratensis

Distribution

[WildflowerSearch map]

[BONAP county map]

[WildflowerSearch map]

[BONAP county map]

Discussion

Disturbed areas, parking lots, lawns, shores. 0–1700m. BR, BW, Casc, Col, CR, Est, Lava, Sisk, WV. CA, ID, NV, WA; throughout southern Canada and US; worldwide. Exotic.

Poa annua is a small but abundant annual with spreading inflorescence branches and oblong anthers. Poa infirma is very similar but has ascending inflorescence branches and shorter, nearly spherical anthers. Poa supina, supine bluegrass, has inflorescences similar to P. annua, but it is a stoloniferous perennial with longer anthers. It is planted on shady golf courses and lawns where it forms dense, spongy turf. It has not been found in the wild in Oregon but is expected to escape here.

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).