OregonFlora: Poa annua vs. Poa

	Poa annua	Poa
	annual bluegrass	bluegrass
Habit	Plants annual, rarely biennial, 2–20(45)cm tall; cespitose.	Plants annual or perennial; cespitose or culms solitary; with or without rhizomes or stolons; usually with bisexual florets but sometimes monoecious or dioecious; basal branching intra- or extravaginal.
Culms	nodes terete or weakly compressed.	usually unbranched above the base.
Basal branching	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 mostly closed to mostly open; ligules membranous, truncate to acuminate; blades flat, folded, or involute; the upper side with 2 longitudinal grooves; tips often prow-shaped.
Inflorescences	1–7(10)cm; branches ascending to spreading or reflexed.	panicles, occasionally reduced and raceme-like; disarticulation above the glumes and beneath the florets.
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.	usually laterally compressed, occasionally nearly round in cross section, usually lanceolate, sometimes ovate, 2–17 mm long, with (1)2–6(13) florets, occasionally forming bulblets.
Glumes	lower glumes smooth, 1-veined.	2, usually shorter than the lowest lemma of the spikelets, usually keeled, 1–3(5)-veined; awnless.
Caryopses		ellipsoidal, 1–4 mm, often shallowly grooved on the ventral side.
Ovaries		glabrous.
Calluses	glabrous.	blunt, glabrous or with a tuft of cobwebby hairs, or with a crown of straight to slightly sinuous hairs.
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.	usually keeled, sometimes rounded over the back, 5(7–11)-veined; margins scarious-hyaline distally; tips truncate or obtuse to acuminate; awnless.
Anthers	0.6–1.1 mm, oblong.
Functional anthers		(1–2)3.
2n	=28.

	Poa annua	Poa
Distribution	[WildflowerSearch map] [BONAP county 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.	Cosmopolitan. Approximately 500 species; 35 species treated in Flora. Poa is the most diverse grass genus in Oregon. Four species have two or more Oregon subspecies, bringing the total to 42 taxa. Bluegrasses are community dominants or important components of dry to moist grasslands, forests, and alpine zones. They are planted for forage as well as for soil stabilization and lawns. Poa annua, P. bulbosa, and some other Poa species may be economically important weeds in crops. Poa pratensis, P. compressa, and P. bulbosa are significant invaders of native ecosystems. The genus Poa exhibits great diversity in breeding systems, though each Poa species is usually consistent in its method of reproduction. Plants may be synoecious (with bisexual florets), gynomonoecious (with both bisexual and pistillate florets on the same plant), sequentially gynomonoecious (with a higher proportion of pistillate florets as the season progresses), gynodioecious (some plants with only pistillate florets and others with bisexual florets), or dioecious (with separate male and female plants). Self-fertilization is common. Some plants set seed apomictically (asexually). One introduced Oregon species produces bulblets asexually in the inflorescence. Many species reproduce vegetatively through spread of rhizomes or stolons. The prevalence of asexual reproduction and selfing in combination with at least occasional outcrossing produces a complex pattern of variation in Poa that can lead to disagreement about species limits. This Poa treatment follows that of Soreng (2007). The most widespread and abundant bluegrasses in Oregon are introduced P. annua, P. bulbosa, and P. pratensis and native P. secunda. Other relatively common species include introduced Poa compressa, P. palustris, and P. trivialis and native P. cusickii and P. wheeleri. All other species are uncommon or rare in Oregon.
Source	Flora of Oregon, volume 1, page 453 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 449 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
Subordinate 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
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: 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

annual bluegrass

bluegrass

Habit

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

Plants annual or perennial; cespitose or culms solitary; with or without rhizomes or stolons; usually with bisexual florets but sometimes monoecious or dioecious; basal branching intra- or extravaginal.

Culms

nodes terete or weakly compressed.

usually unbranched above the base.

Basal branching

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 mostly closed to mostly open;

ligules membranous, truncate to acuminate;

blades flat, folded, or involute; the upper side with 2 longitudinal grooves;

tips often prow-shaped.

Inflorescences

1–7(10)cm;

branches ascending to spreading or reflexed.

panicles, occasionally reduced and raceme-like;

disarticulation above the glumes and beneath the florets.

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.

usually laterally compressed, occasionally nearly round in cross section, usually lanceolate, sometimes ovate, 2–17 mm long, with (1)2–6(13) florets, occasionally forming bulblets.

Glumes

lower glumes smooth, 1-veined.

2, usually shorter than the lowest lemma of the spikelets, usually keeled, 1–3(5)-veined; awnless.

Caryopses

ellipsoidal, 1–4 mm, often shallowly grooved on the ventral side.

Ovaries

glabrous.

Calluses

glabrous.

blunt, glabrous or with a tuft of cobwebby hairs, or with a crown of straight to slightly sinuous hairs.

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.

usually keeled, sometimes rounded over the back, 5(7–11)-veined;

margins scarious-hyaline distally;

tips truncate or obtuse to acuminate; awnless.

Anthers

0.6–1.1 mm, oblong.

Functional anthers

(1–2)3.

=28.

Poa annua

Poa

Distribution

[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.

Cosmopolitan. Approximately 500 species; 35 species treated in Flora.

Poa is the most diverse grass genus in Oregon. Four species have two or more Oregon subspecies, bringing the total to 42 taxa. Bluegrasses are community dominants or important components of dry to moist grasslands, forests, and alpine zones. They are planted for forage as well as for soil stabilization and lawns. Poa annua, P. bulbosa, and some other Poa species may be economically important weeds in crops. Poa pratensis, P. compressa, and P. bulbosa are significant invaders of native ecosystems. The genus Poa exhibits great diversity in breeding systems, though each Poa species is usually consistent in its method of reproduction. Plants may be synoecious (with bisexual florets), gynomonoecious (with both bisexual and pistillate florets on the same plant), sequentially gynomonoecious (with a higher proportion of pistillate florets as the season progresses), gynodioecious (some plants with only pistillate florets and others with bisexual florets), or dioecious (with separate male and female plants). Self-fertilization is common. Some plants set seed apomictically (asexually). One introduced Oregon species produces bulblets asexually in the inflorescence. Many species reproduce vegetatively through spread of rhizomes or stolons. The prevalence of asexual reproduction and selfing in combination with at least occasional outcrossing produces a complex pattern of variation in Poa that can lead to disagreement about species limits. This Poa treatment follows that of Soreng (2007). The most widespread and abundant bluegrasses in Oregon are introduced P. annua, P. bulbosa, and P. pratensis and native P. secunda. Other relatively common species include introduced Poa compressa, P. palustris, and P. trivialis and native P. cusickii and P. wheeleri. All other species are uncommon or rare in Oregon.