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Key to Poa

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1 Plants with well-developed rhizomes; perennial.
..2 Upper stems strongly flattened; [section Tichopoa]
..2 Upper stems terete or nearly so.
....3 Lower nodes of the panicle with 1-3 branches; [section Madropoa]
....3 Lower nodes of the panicle with 4 or more branches; [section Poa]
......4 Basal leaf blades 0.5-1.0 (-1.5) mm wide, involute to folded, relatively stiff; upper leaf blade surfaces sparsely pubescent
......4 Basal leaf blades 1.5-4 mm wide, flat or folded, relatively flexible; upper leaf blade surfaces usually glabrous
1 Plants lacking rhizomes; perennial or annual.
........5 Plants dioecious, the florets unisexual; lemmas and glumes scarious and silvery; [rare introduction in our area]; [section Dioicopoa]
........5 Plants not dioecious, the florets bisexual; lemmas and glumes not notably scarious and silvery; [collectively common and widespread in our area].
..........6 Lemmas not webbed at the base.
............ 7 Annual; culms decumbent to ascending and 1-3 dm long; inflorescence 2-8 cm long, the ascending branches bearing crowded spikelets above the middle; lemmas 2.4-3.4 mm long; [section Micrantherae]
............ 7 Perennial; culms erect, 3-6 dm long; inflorescence 6-15 cm long, the widely spreading branches bearing a few spikelets near the end; lemmas 3.2-4.4 mm long; [section Sylvestres]
..........6 Lemmas webbed at the base.
............ ..8 Culm bulbous-thickened at ground level; [section Arenariae].
............ ....9 Spikelets normally structured, not modified into purplish bulblets
............ ....9 Spikelets (most or all) modified into purplish bulblets
............ ......10 Sheaths and leaf blade undersides glabrous; panicles less diffuse; bulblet bladelets broader
............ ......10 Sheaths and leaf blade undersides hairy; panicles more diffuse; bulblet bladelets narrower and elongated
............ ..8 Culm not bulbous-thickened.
............ ........11 Annual; [section Homalopoa]
............ ............ 13 Nodes of the panicle mostly with 4-8 branches; lemmas pubescent or scabrous on the keel.
............ ............ ..14 Sheaths glabrous; ligule 0.7-2.2 (-3.0) mm long; [section Sylvestres]
............ ............ ..14 Sheaths scabrous; ligule (2.5-) 3-7 mm long; [section Pandemos]
............ ............ 13 Nodes of the panicles mostly with 2 branches; lemmas glabrous on the keel; [section Sylvestres].
............ ............ ....15 Anthers 0.6-0.9 (-1.0) mm long; lemmas broad-acute, obtuse or truncate at the apex, the keel and lateral margins of the lemma forming an apical angle of 42-82 degrees, firm at the tip, the scarious tip absent or up to 0.25 mm long
............ ............ ....15 Anthers 0.9-1.5 mm long; lemmas acute to acuminate at the apex, the keel and lateral margins of the lemma forming an apical angle of 10-47 degrees, pliable at the tip, the scarious tip prominent and 0.25-0.5 mm long
............ ..........12 Marginal veins of the lemma pubescent, at least basally.
............ ............ ......16 Lower nodes of the panicles mostly with (1-) 2-3 branches.
............ ............ ........17 Ligule truncate, 0-1 mm long; first glume 1.7-2.2 mm long, second glume 2.0-2.8 mm long; anthers 0.5-0.7 mm long; [section Oreinos]
............ ............ ........17 Ligule rounded-ovate, 1-2 mm long; first glume 2.5-3.5 mm long, second glume 3.0-3.8 mm long; anthers 1.1-1.4 mm long; [section Sylvestres]
............ ............ ......16 Lower nodes of the panicles mostly with (4-) 5 or more branches.
............ ............ ..........18 Lemmas 5-veined at maturity (intermediate veins well-developed); sheath margin ciliate; ligule 1 (-3) mm long; lower panicle branches distinctly reflexed at maturity; [section Sylvestres]
............ ............ ..........18 Lemmas 3-veined (intermediate veins obscure, even at maturity); sheath margin not ciliate; ligule either (2-) 3-5 mm long or 0.2-1 (-1.5) mm long; lower panicle branches not reflexed at maturity.
............ ............ ............ 19 Glumes narrow, acuminate, approximately as long as the first (lower) lemma; ligule very short, 0.2-0.8(-1) mm long
............ ............ ............ 19 Glumes lanceolate to acute, shorter than the first (lower) lemma; ligules prominent, 0.5-6 mm long.
............ ............ ............ ..20 Ligule 0.5-1.5(-3) mm long, ciliolate; culms erect from a green or tawny base; panicle 3-15 cm long (mostly < 10 cm long); panicle 2.5-4x as long as wide; [section Stenopoa]
............ ............ ............ ..20 Ligule (2-) 3-5 mm long, minutely ciliolate; culms decumbent at the purplish base; panicle 13-30+ cm long (mostly >10 cm long); panicle > 4x as long as wide; [section Pandemos]
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