Poa arctica subsp. aperta
Plants pale green, often glaucous; usually densely tufted, rhizomes usually short, usually well developed. Culms 20-60 cm, several together, wiry, bases decumbent. Sheaths closed for (1/6)1/5 – 1/3 their length; ligules 3-7 mm, sparsely to moderately scabrous, acute; blades 1.5-2.5 mm wide, flat, folded, or somewhat involute. Panicles 4-15 cm, erect, loosely contracted or open, with 1-3 branches per node; branches ascending or widely spreading, fairly stout, fairly straight, smooth to very sparsely scabrous, proximal branches 1/4-1/2 the panicle length. Spikelets narrowly lanceolate to lanceolate, not bulbiferous; florets 2-3(4), normal; rachilla internodes usually glabrous, infrequently sparsely softly puberulent; calluses glabrous or webbed, hairs to 1/4 the lemma length; lemmas 3-4.5(6) mm; palea keels usually softly puberulent to long-villous at midlength, infrequently glabrous, intercostal regions usually softly puberulent; anthers aborted late in development or fully developed. 2n = 98+1.
Discussion
Poa arctica subsp. aperta is restricted to subalpine and low alpine habitats on the Wasatch Escarpment and high mountains of the Colorado Plateau in southern Utah, and the Rocky Mountains of southern Colorado and northern New Mexico. Many reports of P. arida (p. 599) growing west of the Rocky Mountains are based on misidentification of this subspecies. Poa arctica subsp. aperta may reflect introgression of genes from P. secunda (p. 586) into P. arctica. It has softer leaves, and is more densely hairy between the lemma veins and the palea keels, than subsp. arctica. It can be distinguished from subsp. grayana by its more wiry culms, and less contracted panicles with straighter branches.
Selected References
None.