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Key to Andropogon

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1 Pedicellate spikelet staminate, as large as the sessile, fertile spikelet; sessile spikelets > 7 mm long; [section Andropogon]
..2 Upper lemma of the sterile spikelet with an awn (7.5-) 10-25 mm long; rhizomes short or absent (with internodes usually < 2 mm long; ligule 0.4-2.5 mm long; anthers < 3.8 mm long; inflorescences hairy but not densely long-villous; [widespread in most of our area]
..2 Upper lemma of the sterile spikelet with an awn 0-6 (-11) mm long; rhizomes well-developed, creeping, with internodes often > 20 mm long; ligule (0.9-) 3.0-4.5 mm long; anthers > 3.8 mm long; inflorescences densely long-villous with white to yellow hairs, the axes somewhat obscured by the density of hairs; [western edge of our area, rarely introduced eastwards]
1 Pedicellate spikelet sterile, vestigial or absent; sessile spikelets < 7 mm long; [section Leptopogon].
....3 Leaves strongly glaucous (often nearly white with a powdery wax that can be rubbed off on the fingers), glabrous.
......4 Ligule membrane (0.9-) 1.5 (-2.0) mm long, with cilia 0-0.2 mm long; leaf blades usually (33-) avg. 40 (-75) cm long; pubescence beneath raceme sheaths moderate to dense; raceme sheaths (2.0-) 2.4-3.6 (-4.4) cm long, (1.3-) 2.0-2.5 (-3.0) mm wide
......4 Ligule membrane (0.2-) 0.4 (-0.5) mm long, with cilia 0.3-1.2 mm long; leaf blades (12-) avg. 19 (-38) cm long; pubescence beneath raceme sheaths absent to dense; raceme sheaths (2.1-) 2.9-4.3 (-6.0) cm long, (2.7-) 3.1-3.8 (-5.5) mm wide.
........5 Summit of branchlet below attachment of raceme sheath glabrous; raceme sheaths (2.1-) 2.6-3.8 (-4.9) cm long; spikelets (2.6-) 3.2-3.5 (-3.9) mm long; racemes (1.4-) 1.7-2.4 (-3.2) cm long; leaves 2-5 mm wide, averaging 3.5 mm; upper floret lemma awn 0.6-1.5 mm long, averaging 1.1 mm
........5 Summit of branchlet below attachment of raceme sheath pubescent with hairs 2-4 mm long; raceme sheaths (2.4-) 3.2-4.8 (-6.0) cm long; spikelets (3.0-) 3.5-3.9 (-4.4) mm long; racemes (1.5-) 2.0-3.0 (-4.0) cm long; leaves 2.5-6.5 mm wide, averaging 5 mm; upper floret lemma awn 0.9-2.1 mm long, averaging 1.4 mm
....3 Leaves green (to somewhat glaucous, but never powdery white), pubescent or glabrous.
..........6 Upper culm sheaths distinctly broadened and strongly overlapping, often largely hiding the raceme sheaths before senescence (but in some forms with the raceme sheaths strongly exserted); culms mostly < 1 m tall (to 1.4 m tall)
..........6 Upper culm sheaths reduced, not strongly overlapping, not hiding the raceme sheaths after anthesis; culms mostly > 1 m tall (except A. perangustatus, A. tracyi, A. subtenuis, and small forms of A. virginicus).
............ 7 Many or all peduncles longer than the subtending raceme sheaths at maturity, racemes then fully exserted above the apex of the raceme sheath.
............ ..8 Sessile spikelets 3-4 mm long, unawned; [s. FL]
............ ..8 Sessile spikelets (3.8-) 4.4-8.4 mm long, with an awn; [collectively widespread].
............ ....9 Inflorescence branches arching outward in pronounced curves; racemes (1.2-) 1.5-2.1 (-2.6) cm long; lemma awns (2-) avg. 7 (-11) mm long; spikelets (4.1-) 4.4-4.6 (-5.0) mm long
............ ....9 Inflorescence branches erect; racemes (2.2-) 2.5-6 cm long; lemma awns 5-20 mm long; spikelets (3.8-) 4.4-6.5 (-7.5) mm long.
............ ......10 Stems < 0.9 m tall; leaves < 2 mm wide; some racemes usually fully included within raceme sheaths at maturity on peduncles < 10 mm long; anthers often marcescent
............ ......10 Stems > 1 m tall; leaves usually > 3 mm wide; racemes rarely included within raceme sheaths at maturity, peduncles rarely < 15 mm long; anthers rarely marcescent.
............ ........11 Leaf sheaths scabrous; inflorescence units usually 50-200 per culm; [of dry, deep sand habitats]
............ ........11 Leaf sheaths smooth or nearly so; inflorescence units usually 3-50 per culm; [of various habitats].
............ ..........12 Sessile spikelets 4-5 mm long; lemma awns mostly 5-10 mm long; rachis internode pubescence more or less evenly distributed along the internode; inflorescence peduncles mostly less than 9 cm long.
............ ............ 13 Basal leaf sheaths and upper surface of basal leaf blades appressed-pubescent, often appearing silvery-silky; basal leaf blades mostly 5-6 mm wide; culms 2.5-4.5 mm in diameter; inflorescence units usually 30-50 per culm, each with 2-4 racemes
............ ............ 13 Basal leaf sheaths moderately to densely villous, but not silvery-silky; basal leaf blades glabrous to sparsely pubescent with spreading hairs, 2-2.5 mm wide; culms 1.5-2.0 mm in diameter; inflorescence units usually less than 15 per culm, all with 2 racemes
............ ..........12 Sessile spikelets 5-7 mm long; lemma awns mostly 10-25 mm long; rachis internode with longest hairs concentrated towards its apex; inflorescence peduncles 10-17 cm long.
............ ............ ..14 First glume nerveless and glabrous or nearly so between the keels; raceme internodes with longest hairs 8-9 mm long, somewhat obscuring the spikelets; lemma awns mostly more than 18 mm long; pedicellate spikelet vestigial, 1-2 mm long
............ ............ ..14 First glume 2-3 nerved between the keels, its surface moderately to densely scabridulous; raceme internodes with longest hairs 3-6 mm long, not obscuring the spikelets; lemma awns mostly less than 18 mm long; pedicellate spikelets evident, 2-4 mm long.
............ ............ ....15 Basal leaf sheaths and lower surface of basal leaf blades green or bluish-green, not glaucous; culm internodes not glaucous; culms mostly 120-170 cm tall, usually with 10-20 inflorescence units per culm
............ ............ ....15 Basal leaf sheaths and lower surface of basal leaf blades bluish-glaucous; culm internodes slightly to evidently glaucous; culms mostly over 180 cm tall, usually with 10 or fewer inflorescence units per culm
............ 7 Peduncles all shorter than the subtending raceme sheaths at maturity, at least the bases of the racemes not exserted above the apex of the raceme sheath.
............ ............ ......16 Inflorescence units with (2-) 4-7 (-13) racemes; raceme sheaths (4.1-) 5.3-8.0 (-10-1) mm wide; hairs of the rachis internode and pedicel yellow-tawny when dry
............ ............ ......16 Inflorescence units with 2-5 (-7) racemes; raceme sheaths (1.5-) 2.0-4.8 (-6.3) mm wide; hairs of the rachis internode and pedicel gray to whitish when dry.
............ ............ ........17 Post-flowering peduncles (at least some of them) > 15 mm long.
............ ............ ..........18 Culm sheaths antrorsely scabrous (often hirsute as well).
............ ............ ............ 19 Racemes (2.0-) 2.5-3.7 (-4.5) cm long; [of upland xeric, sandy habitats, s. GA southwards]
............ ............ ............ 19 Racemes (1.0-) 1.7-2.5 (-3.5) cm long; [of wetland habitats, at least seasonally saturated, collectively widespread in our area].
............ ............ ............ ..20 Ligules (1.0-) 1.2 (-2.0) mm long, with cilia 0-0.3 mm long; keels of first glume scabrous only above middle
............ ............ ............ ..20 Ligules (0.6-) 0.8 (-1.3) mm long, with cilia 0.2-0.9 mm long; keels of first glume often scabrous below middle
............ ............ ..........18 Culm sheaths not scabrous (often hirsute).
............ ............ ............ ....21 Culms usually > 1.2 m tall; leaf blades often > 30 cm long and > 3 mm wide; inflorescence units usually > 20/culm.
............ ............ ............ ......22 Inflorescence branches arching outward in pronounced curves; awn mostly < 1 cm long; spikelets (4.1-) 4.4-4.6 (-5.0) mm long; anther > 1.7 mm long
............ ............ ............ ......22 Inflorescence branches erect; awn mostly >1 cm long; spikelets (3.0-) 3.3-3.8 (-4.5) mm long; anther < 1.5 mm long.
............ ............ ............ ........23 Raceme sheaths (1.7-) 2.4-3.1 (-4.0) mm wide; keels of first glume scabrous only above middle; culms < 1.7 m tall; leaves < 35 cm long and 5.5 mm wide
............ ............ ............ ........23 Raceme sheaths (1.5-) 2.0-2.5 (-3.0) mm wide; keels of first glume often scabrous below middle; culms to 2.5 m tall; leaves to 109 cm long and 9.5 mm wide
............ ............ ............ ....21 Culms < 1.2 m tall; leaf blades < 30 cm long and < 3 mm wide; inflorescence units rarely > 20/culm.
............ ............ ............ ..........24 Raceme sheaths (2.2-) 2.5-3.8 (-4.5) cm long; spikelets (3.0-) 3.3-3.6 (-4.0) mm long; leaf blades (2.5-) 3.6 (-5.5) mm wide
............ ............ ............ ..........24 Raceme sheaths (2.6-) 4.9-7.9 (-9.5) cm long; spikelets (3.0-) 3.4-5.1 (-5.5) mm long; leaf blades (0.8-) 1.8-2.0 (-3.0) mm wide.
............ ............ ............ ............ 25 Ligules (0.2-) 0.4 (-0.5) mm long, with cilia (0.1-) 0.2-0.8 mm long; spikelets (4-) 4.8-5.0 (5.5) mm long; racemes 2 per inflorescence unit
............ ............ ............ ............ 25 Ligules (0.4-) 0.6-1.1 (-1.5) mm long, with cilia 0-0.3 mm long; spikelets (3-) 3.4-5.1 (-5.5) mm long; racemes 2-4 per inflorescence unit.
............ ............ ............ ............ ..26 Ligules (0.4-) 0.6 (-0.8) mm long, with cilia 0-0.3 mm long
............ ............ ............ ............ ..26 Ligules (0.8-) 1.1 (-1.5) mm long, with cilia 0-0.1 mm long
............ ............ ........17 Post-flowering peduncles < 10 mm long.
............ ............ ............ ............ ....27 Culm sheaths antrorsely scabrous (often hirsute as well); leaf blades usually > 35 cm long.
............ ............ ............ ............ ......28 Ligules (0.6-) 0.8 (-1.3) mm long (usually < 1 mm long), with cilia 0.2-0.9 mm long; raceme sheaths (1.5-) 2.0-2.5 (-3.0) mm wide (usually < 2.5 mm wide); keels of first glume often scabrous below the middle
............ ............ ............ ............ ......28 Ligules (0.7-) 1.2 (-2.2) mm long (usually > 1 mm long), with cilia 0.0-0.3 mm long; raceme sheaths (2.0-) 2.4-3.4 (-4.7) mm wide (usually > 2.5 mm wide); keels of first glume scabrous only above the middle, smooth below.
............ ............ ............ ............ ........29 Inflorescences oblong to obpyramidal; spikelets (3.8-) 4.1-4.4 (-5.0) mm long; anthers usually not marcescent within spikelet; mature peduncles (4 -) 11-35 (-60) mm long (usually some of them > 10 mm long)
............ ............ ............ ............ ........29 Inflorescences (linear to) oblong; spikelets (3.4-) 3.6-3.8 (-4.6) mm long; anthers usually marcescent within spikelets; mature peduncles (2-) 3-5 (-8) mm long
............ ............ ............ ............ ....27 Culm sheaths not scabrous (often hirsute); leaf blades < 35 cm long (except in A. glomeratus var. pumilus).
............ ............ ............ ............ ..........30 Raceme sheaths (2-) 2.4-4.6 (-6.7) × 1.5-4.5 (-6.0) mm.
............ ............ ............ ............ ............ ..32 Ligules (0.8-) 1.1 (-1.5) mm long, with cilia 0-0.1 mm long; basal leaves often filiform, < 1.5 mm wide, strongly erect
............ ............ ............ ............ ............ ..32 Ligules (0.2-) 0.5 (-0.8) mm long, with cilia 0.2-1.3 mm long; basal leaves usually > 2 mm wide, soon arching.
............ ............ ............ ............ ............ ....33 Culm internodes green (or glaucous just below the node only); raceme sheaths (2.2-) 2.5-3.8 (-4.5) cm long, (1.7-) 2.4-3.1 (-4.0) mm wide; peduncles (1-) 4-9 (-30) mm long; racemes 2 (-3) per inflorescence unit
............ ............ ............ ............ ............ ....33 Culm internodes glaucous; raceme sheaths (2.8-) 3.3-7.9 (-9.5) cm long, (1.5-) 2.5-4.3 (-5.2) mm wide; peduncles (1-) 3-25 (-50) mm long; racemes 2-4 (-7) per inflorescence unit, at least some inflorescence units (especially at culm and branch apices) with 3 or more racemes.
............ ............ ............ ............ ............ ......34 Stems < 1 m tall; inflorescence units < 14 per stem; spikelets (3.5-) 4.0-4.5 (-5.2 mm long; raceme sheaths (4.0-) 4.9-7.9 (-9.5) cm long, (1.5-) 2.5-4.3 (-5.0) mm wide; peduncles (1-) 5-25 (-50) mm long; racemes 2-4 (-7) per inflorescence unit, at least some inflorescence units (especially at culm and branch apices) with 3 or more racemes
............ ............ ............ ............ ............ ......34 Stems > 1 m tall; inflorescence units usually > 14 per stem; spikelets (3.0-) 3.5-3.7 (-4.2) mm long; raceme sheaths (2.8-) 3.3-4.7 (-6.7) cm long, (3.0-) 3.2-3.8 (-5.2) mm wide; peduncles (2-) 3-4 (-6) mm long; racemes 2-4 (-7) per inflorescence unit, at least some inflorescence units (especially at culm and branch apices) with 3 or more racemes
............ ............ ............ ............ ............ 31 Leaves pubescent, at least on the margin near the collar.
............ ............ ............ ............ ............ ........35 Keels of first glume often scabrous below the middle; leaves usually > 44 cm long
............ ............ ............ ............ ............ ........35 Keels of first glume scabrous only above middle; leaves usually < 31 cm long.
............ ............ ............ ............ ............ ..........36 Pubescence of young culm sheaths appressed; spikelets usually > 4 mm long; hairs on rachis internode and sterile pedicel dense, long; callus hairs 1.5-5 mm long
............ ............ ............ ............ ............ ..........36 Pubescence of young culm sheaths spreading; spikelets mostly < 4 mm long; hairs on rachis internode and sterile pedicel rather sparse and short; callus hairs 1-2.5 mm long.
............ ............ ............ ............ ............ ............ 37 Raceme sheaths (2.2-) 2.5-3.8 (-4.5) cm long, (1.7-) 2.4-3.1 (-4.0) mm wide; racemes 2 (3) per inflorescence unit; spikelets (3.0-) 3.3-3.6 (-4.0) mm long
............ ............ ............ ............ ............ ............ 37 Raceme sheaths (2.3-) 3.4-5.2 (-6.7) cm long, (2.7-) 3.3-4.0 (-5.5) mm wide; racemes 2-5 (-7) per inflorescence unit; spikelets (2.9-) 3.7-3.9 (-4.7) mm long
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