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Poa

See list of 14 species in this genus

Ligule measurements for the key should be performed on the upper one or two leaves of the stem. Assessment of pubescence (of any kind) within the spikelet should occur on the lower florets. Reference: Soreng (2007).

  • 1a. Plants annual, with soft stem bases
    • 2a. Callus of the lemma without arachnoid hairs; reproductive stems mostly decumbent to ascending, sometimes even rooting at the lower nodes [Fig. 257]; anthers (0.5–) 0.8–1 mm long; all 5 veins of the lemma prominent
    • 2b. Callus of the lemma with arachnoid hairs; reproductive stems strongly ascending to erect; anthers 0.1–0.2 mm long; only 3 veins of the lemma prominent, the intermediate 2 veins inconspicuous
  • 1b. Plants perennial, with firm stem bases and persistent, dried leaves from the previous season
    • 3a. Many of the florets converted to bulbils with overlapping scales, some of the scales prolonged into narrow, elongate tips 5–15 mm long [Fig. 258]; new shoots bulbous at 
the base
    • 3b. None of the florets converted to bulbils, lacking narrow, elongate tips; new shoots without bulbous bases
      • 4a. Plants with elongate, slender rhizomes
        • 5a. Stems strongly compressed, with 3–7 leaves; panicle branches mostly 
2 per node [Fig. 259]; only 3 veins of the lemma prominent, the intermediate 
2 veins inconspicuous
        • 5b. Stems terete to slightly compressed, with 2–4 leaves; panicle branches 2–5 per node [Fig. 262]; all 5 veins of the lemma prominent
      • 4b. Plants without rhizomes (though sometimes with stolons)
        • 6a. Marginal veins of the lemma pubescent, at least toward the base [Fig. 261]
            • 8a. Glumes narrow-lanceolate, long-acuminate at the apex [Fig. 260], the upper one 4.6–6.2 times as long as wide in sideview and shorter than to subequal in length to the adjacent lemma; uppermost nodes on stem positioned at ½ to ¾ stem height; ligules 0.2–0.7 (–1) mm long; plants often forming extensive colonies in the understory of forested communities
            • 8b. Glumes lanceolate to broad-lanceolate, acute to short-acuminate at the apex, the upper one 3.1–5 times as long as wide in side view and shorter than adjacent lemma; uppermost nodes on stem positioned at to stem height; ligules 0.5–1.5 mm long; plants not forming colonies, the individuals more scattered (in part)
            • 9a. Panicle (9–) 13–30 cm tall, with spreading to spreading-ascending 
branches that often arch or nod in the distal portion; internodes of the rachilla glabrous; plants primarily of temperate and low elevation mesic to hydric 
soils, sometimes weakly stoloniferous and sometimes with stems branched above the base
            • 9b. Panicle 1–10 (–15) cm tall, with ascending to erect, relatively straight branches (some branches often ± spreading in P. interior); internodes of rachilla minutely pubescent (view at 30 × magnification) or glabrous inP. laxa and sometimes P. interior; plants primarily of boreal, subalpine, and alpine cliffs, talus, and plateaus, without stolons and with simple stems above the base
              • 10a. Anthers 0.7–0.9 mm long; ligules 2.5–3.5 mm long; branches of panicle smooth or sparsely scabrous on the angles, produced 1–3 at each node, usually paired
              • 10b. Anthers 1–2.2 (–2.5) mm long; ligules 0.5–2 (–2.5) mm long; branches of panicle moderately to densely scabrous on the angles (rarely smooth for much of length), produced 2–5 at each node
                • 11a. Lemmas usually at least sparsely pubescent on the lateral veins (often some within a panicle glabrous); uppermost stem node usually positioned at 1⁄10 to stem height; reproductive stems with 0 (–1) exposed nodes, the nodes usually concealed within the leaf sheaths; ligules (1–) 1.2–2 (–2.5) mm long; mature, intact spikelets (1.7–) 2–3.9 mm wide in side-view
                • 11b. Lemmas glabrous on the lateral veins; uppermost stem node usually positioned at to stem height; reproductive stems with (0–) 1 or 
2 (–3) exposed nodes; ligules 0.5–1.5 mm long; mature, intact spikelets 1.2–2 (–2.6) mm wide in side view (in part)
        • 6b. Marginal veins of the lemma glabrous [Fig. 256]

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