Poa interior
Plants perennial; green or less often glaucous; densely tufted, not stoloniferous, not rhizomatous. Basal branching all or mostly extravaginal. Culms 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. Sheaths 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. Panicles (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. Spikelets 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. Glumes 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. 2n = 28, 42, 56.
Discussion
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.
Selected References
None.