Poa arctica
Poa interior
arctic bluegrass
inland bluegrass, interior blue grass, woods blue grass
7.5-60 cm, slender to stout, terete or weakly compressed, bases usually decumbent, not branching above the bases;
nodes terete, proximal nodes usually not exserted, 0-2 exserted above.
5-80 cm, usually slender, mostly erect or ascending, several to many arising together;
nodes terete or slightly compressed, (0)1-2(3) exserted, top node usually at 1/3 – 3/5 the culm length.
closed for (1/6)1/5 – 2/5 their length, terete, glabrous, smooth or sparsely scabrous, bases of basal sheaths glabrous, distal sheath lengths 1.4-4(5.3) times blade lengths;
collars smooth, glabrous;
ligules (1)2-7 mm, glabrous, smooth or sparsely to infrequently moderately scabrous, apices usually rounded to obtuse or acute, rarely truncate, entire or lacerate;
blades 1-6 mm wide, flat or folded, somewhat involute, smooth, glabrous, apices broadly prow-shaped, cauline blades subequal or gradually reduced distally, flag leaf blades 0.7-9 cm.
closed for 1/10 – 1/5 their length, terete, bases of basal sheaths glabrous, distal sheath lengths (0.6)0.88-1.64 times blade lengths;
ligules 0.5-1.5(3) mm, sparsely to densely scabrous, apices truncate to obtuse, ciliolate;
blades 0.8-3 mm wide, mostly flat, thin, soft, appressed or abruptly ascending to spreading, straight or somewhat lax, apices narrowly prow-shaped.
mainly extravaginal.
all or mostly extravaginal.
(2)3.5-15 cm, ovoid to broadly pyramidal, usually open, sparse, with 10-40(60) spikelets, proximal internodes shorter than 1.5(3) cm, with (1)2-5 branches per node;
branches 1.5-6 cm, spreading soon after emergence from the sheath, thin, sinuous, and flexuous to fairly stout and straight, terete, smooth or sparsely to infrequently moderately scabrous, with (1)2-5 spikelets, the spikelets not crowded.
(1.5)3-15(17) cm, lengths generally 2.5-4 times widths at maturity, usually erect, lax in shade forms, narrowly lanceoloid to ovoid, sparsely to moderately congested;
nodes with 2-5 branches;
branches 0.4-8(9) cm long, 1/4-1/2 the panicle length, ascending to widely spreading, fairly straight, slender to moderately stout, angled, angles moderately to densely scabrous.
(3.5) 4.5-8 mm, lengths to 3.5 times widths, laterally compressed, sometimes bulbiferous;
florets (2)3-6, infrequently bulb-forming;
rachilla internodes smooth or muriculate, proximal internodes glabrous or sparsely softly puberulent to long-villous.
3-6 mm, lengths 2-3 times widths, lanceolate to narrowly ovate, laterally compressed, usually not glaucous;
florets (1)2-3(5);
rachilla internodes usually shorter than 1 mm, smooth, muriculate, or scabrous, glabrous, hispidulous, or sparsely to densely puberulent, proximal internodes frequently curved.
lanceolate to broadly lanceolate, distinctly or weakly keeled, keels usually smooth, sometimes sparsely scabrous distally, lateral veins usually moderately pronounced;
lower glumes (3)3.5-5(6) mm, 3-veined;
upper glumes 3.5-5.5(6.5) mm, nearly equaling to slightly exceeding the lowest lemmas, or distinctly shorter;
calluses glabrous or webbed, hairs sparse and short to over 1/3 – 2/3 the lemma length;
lemmas (2.7)3-6(7) mm, lanceolate to broadly lanceolate, usually strongly purple, distinctly keeled, keels, marginal veins, and lateral veins long-villous, hairs on the lateral veins sometimes shorter, lateral veins prominent, intercostal regions short-villous to softly puberulent at least near the base, glabrous elsewhere, smooth to weakly muriculate and/or usually sparsely scabrous, infrequently moderately scabrous, margins broadly hyaline, glabrous, apices acute;
palea keels usually short- to long-villous for most of their length, rarely nearly glabrous and scabrous, intercostal regions broad, usually at least sparsely softly puberulent, rarely glabrous, apices scabrous;
anthers 1.4-2.5 mm, sometimes aborted late in development.
lanceolate to broadly lanceolate, distinctly keeled, keels smooth or sparsely scabrous;
lower glumes 3-veined, long- or abruptly tapered to a slender point, lengths 4.5-6.3 times widths;
calluses usually webbed, infrequently glabrous in depauperate alpine specimens, webs usually scant, less than 1/2(2/3) the lemma length, frequently minute;
lemmas 2.4-4 mm, lanceolate, distinctly keeled, straight or gradually arched, not abruptly inwardly arched at the junction with the scarious apices, keels and marginal veins short-villous, hairs extending 2/3 – 3/4 the keel length, lateral veins usually glabrous, rarely sparsely puberulent, obscure, intercostal regions smooth, sometimes weakly muriculate, glabrous, margins not or slightly inrolled, glabrous, apices acute, usually partially bronze-colored;
palea keels scabrous, intercostal regions glabrous;
anthers (1.1)1.3-2.5 mm.
= 36, 42, 56, 60, 62-68, 70, ca. 72, 74-76, 78-80, 82-84, 86, 88, 99, 106.
= 28, 42, 56.
Poa arctica
Poa interior
Poa arctica is a common circumboreal species of arctic and alpine regions, growing mainly in mesic to subhydric, acidic tundra and alpine meadows, and on rocky slopes. It extends south in the Rocky Mountains to New Mexico. The frequency of sterile anthers in plants of the high arctic suggests that P. arctica is sometimes apomictic in that region. Over most of the rest of its range, P. arctica usually develops normal anthers. This and isozyme data for populations from alpine and low arctic regions suggest sexual reproduction is common in these habitats.
The most reliable way to distinguish Poa arctica from P. pratensis (p. 522), particularly subsp. alpigena, is by the wider paleas and the presence of hairs between the palea keels. Bulbiferous forms of P. arctica differ from P. stenantha var. vivipara (p. 594) in not being glaucous, and in having rhizomes and terete, smooth panicle branches. Poa xgaspensis (p. 601) also resembles P. arctica, but it has sharply keeled, more scabrous glumes and a spikelet shape that is intermediate between P. pratensis and P. alpina (p. 518). Poa arctica forms natural hybrids with both P. pratensis and P. secunda (p. 586).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Poa interior, a native species, grows from Alaska to western Quebec and New York, south to Arizona and New Mexico. It is restricted to the Flora region. It is fairly common from boreal forests to low alpine habitats of the Rocky Mountains. It grows in subxeric to mesic habitats, such as mossy rocks and scree, usually in forests. It is usually tetraploid.
In alpine habitats, Poa interior is often quite short, and often sympatric with P. glauca (see next). It is most reliably distinguished from P. glauca by lemmas that are glabrous between the marginal veins and keels or, rarely, sparsely puberulent on the lateral veins. It usually also differs from P. glauca subsp. rupicola in having at least a few hairs on its calluses. It can be distinguished from P. nemoralis (see previous) by its longer ligules, lower top culm node, and wider glumes and lemmas. It is sometimes difficult to distinguish from P. palustris (p. 574), but differs in having lemmas with wider hyaline margins and straight or gradually arched keels, a densely tufted habit, and scantly webbed calluses.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants lacking well-developed rhizomes; anthers aborted late in development; plants of the high arctic | subsp. caespitans |
1. Plants usually with well-developed rhizomes; anthers normal or plants not of the high arctic. | → 2 |
2. Panicles erect, the branches relatively stout, fairly straight; longest branches of the lowest panicle nodes 1/4-1/2 the length of the panicles; culms wiry, usually several together; calluses glabrous or shortly webbed; paleas sometimes glabrous; plants glaucous, growing in the southern Rocky-Mountains and adjacent portions of the Intermountain region | subsp. aperta |
2. Panicles lax to erect, the branches slender, flexuous to fairly stout and straight; longest branches of the lowest panicle nodes 2/5 – 3/5 the length of the panicles; culms slender to stout, varying from solitary to several together; calluses glabrous or webbed, the hairs usually more than 1/2 as long as the lemmas; paleas pubescent; plants sometimes glaucous, widespread in distribution. | → 3 |
3. Calluses glabrous; spikelets not bulbiferous | subsp. grayana |
3. Calluses webbed, often copiously so, sometimes glabrous in bulbiferous spikelets; spikelets sometimes bulbiferous. | → 4 |
4. Spikelets (5)6-8 mm long; lemmas 4-6 mm long; blades 2-6 mm wide; rachillas usually hairy; plants primarily of the western arctic, extending to northwestern British Columbia | subsp. lanata |
4. Spikelets (3.5)4-7 mm long; lemmas (2.7)3-4.5 mm long; blades 1.5-3 mm wide; rachillas commonly glabrous; plants widespread | subsp. arctica |
BC
WA
CalFlora
Flora NW
PNW Herbaria
WildflowerSearch
iNaturalist
USDA Plants Database
