OregonFlora: Poa lettermanii vs. Poa

	Poa lettermanii	Poa
	Letterman's bluegrass	bluegrass
Habit	Plants perennial, 1–12 cm tall; densely 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		usually unbranched above the base.
Basal branching	intra- and extravaginal or mainly intravaginal.
Leaves	sheaths closed to 25% of their length; ligules 1–3 mm; blades flat or folded, or slightly inrolled, 0.5–2 mm wide.	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	erect, contracted, 1–3 cm long, usually exserted from the sheaths; branches erect to steeply ascending; slender; to 1.5 cm.	panicles, occasionally reduced and raceme-like; disarticulation above the glumes and beneath the florets.
Spikelets	3–4 mm, green or purple; florets 2–3; rachilla internodes less than 1 mm long; smooth.	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	lanceolate to broadly lanceolate, 2.4– 3.6(4) mm, usually equaling or exceeding the lowest lemma, frequently exceeding the upper florets; lower glumes 3-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, 2.5–3 mm long, distinctly keeled; thin, glabrous; keels and marginal veins rarely sparsely puberulent; tips acute.	usually keeled, sometimes rounded over the back, 5(7–11)-veined; margins scarious-hyaline distally; tips truncate or obtuse to acuminate; awnless.
Anthers	0.2–0.8 mm.
Functional anthers		(1–2)3.
2n	=14.

	Poa lettermanii	Poa
Distribution	[WildflowerSearch map] [BONAP county map]	[BONAP county map]
Discussion	Rocky alpine ridges and ledges. 2900–3100m. Casc. CA, ID, NV, WA; north to British Columbia, east to CO. Native. This is a small, cespitose, alpine bluegrass, most similar to P. suksdorfii. Both have subequal glumes that tend to be longer than the lowest lemma, but P. suksdorfii has larger spikelets with longer glumes. In Oregon, P. lettermanii is known only from high elevation on South Sister in the central Cascades.	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 459 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. 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. 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

Letterman's bluegrass

bluegrass

Habit

Plants perennial, 1–12 cm tall; densely 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

usually unbranched above the base.

Basal branching

intra- and extravaginal or mainly intravaginal.

Leaves

sheaths closed to 25% of their length;

ligules 1–3 mm;

blades flat or folded, or slightly inrolled, 0.5–2 mm wide.

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

erect, contracted, 1–3 cm long, usually exserted from the sheaths;

branches erect to steeply ascending; slender; to 1.5 cm.

panicles, occasionally reduced and raceme-like;

disarticulation above the glumes and beneath the florets.

Spikelets

3–4 mm, green or purple;

florets 2–3;

rachilla internodes less than 1 mm long; smooth.

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

lanceolate to broadly lanceolate, 2.4– 3.6(4) mm, usually equaling or exceeding the lowest lemma, frequently exceeding the upper florets;

lower glumes 3-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, 2.5–3 mm long, distinctly keeled; thin, glabrous;

keels and marginal veins rarely sparsely puberulent;

tips acute.

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

margins scarious-hyaline distally;

tips truncate or obtuse to acuminate; awnless.

Anthers

0.2–0.8 mm.

Functional anthers

(1–2)3.

=14.

Poa lettermanii

Poa

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Rocky alpine ridges and ledges. 2900–3100m. Casc. CA, ID, NV, WA; north to British Columbia, east to CO. Native.

This is a small, cespitose, alpine bluegrass, most similar to P. suksdorfii. Both have subequal glumes that tend to be longer than the lowest lemma, but P. suksdorfii has larger spikelets with longer glumes. In Oregon, P. lettermanii is known only from high elevation on South Sister in the central Cascades.

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.