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Key to Muhlenbergia

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1 Panicle open and diffuse, > 4 cm broad, ultimately appearing broad and not spikelike; the spikelets borne separately on slender or capillary pedicels longer than the lemmas or borne tightly and appressed on diverging spikelike branches.
..2 Spikelets mostly sessile, not borne on capillary pedicels, tightly appressed to the panicle branches; panicle branches strongly divergent; [subgenus Pseudosporobolus]
..2 Spikelets borne on slender or capillary pedicels (pedicellate), not appressed tightly to panicle branches, individual panicle branches not spikelike; branches primarily ascending (sometimes weakly divergent).
....3 Spikelets 1.1-2.2 mm long; spikelets with 1 floret, occasionally 2 or 3.
......4 Plants without rhizomes, instead tufted with erect culms (bunched); Spikelets 1.5-2 mm long; lemmas awnless; [subgenus Pseudosporobolus]
......4 Plants not cespitose, rhizomatous, the rhizomes prominent, creeping, and covered with imbricate scales; awns of the lemma 1.1-2.2 mm long.
........5 Culms compressed-keeled, ascending; blades conduplicate (folded lengthwise), 6-20 cm long; panicles cylindrical, 10-28 cm long, 4-8 cm wide; [subgenus “incertae sedis”]
........5 Culms terete to somewhat compressed-keeled near the base, decumbent-ascending; blades usually flat, occasionally conduplicate, 2-7(-11) cm long; panicles ovoid, 6-21 cm long, 4-16 cm wide; [subgenus Pseudosporobolus]
....3 Spikelets 2.5-5 mm long (excluding awns); spikelets with 1 floret [subgenus Trichochloa].
..........6 Lemma awn 0-1.5 (-4) mm long; glume bodies (1.1-) 2.0-3.3 (-3.6) mm long, < ½ as long as the lemma bodies, acuminate, not awned (rarely the second with a short awn < 0.6 mm long); spikelets usually brown or bronze (when fresh); basal sheaths usually very fibrous
..........6 Lemma awn (2-) 3-35 mm long; glume bodies (0.3-) 0.7-1.7 (-2.4) mm long, > ½ as long as the lemma body, one or both glumes sometimes awned; spikelets usually purple (when fresh); basal sheaths rarely strongly fibrous.
............ 7 Lemma awn (2-) 3-13 (-18) mm long, first glume awnless (or rarely with an awn to 3.2 mm long), second glume awnless (or rarely with an awn up to 5.0 mm long), palea awnless; lemma lacking setaceous teeth flanking the awn; flowering late Aug-Oct; [widespread in our area, particularly in rocky, clayey, or sandy glades, barrens, and woodlands with prairie affinities]
............ 7 Lemma awn (8-) 12-26 (-35) mm long, first glume awn (0.5-) 1-7 (-10) mm long, second glume awn (1-) 5-19 (-25) mm long, palea awn-tipped; lemma with two setaceous teeth flanking the awn, the teeth 0.5-2.5 (-4.7) mm long; flowering Oct-Nov; [sandy maritime situations on barrier islands of the outer Coastal Plain]
1 Panicle slender, dense, < 2.5 cm broad, ultimately appearing spikelike, the spikelets sessile or on non-capillary pedicels shorter than the lemmas; [subgenus Muhlenbergia].
............ ..8 Glumes minute, 0-0.5 mm long; plant lacking rhizomes; culms weak, decumbent and cespitosely branching in their lower portions, rooting at the nodes, the upper portions erect and sparsely branched
............ ..8 Glumes well-developed, 1-8 mm long; plant with scaly rhizomes (except for M. cuspidata); culms firm (rarely sprawling), few or solitary (rarely forming dense colonies).
............ ....9 Glumes 3-8 mm long (tapered to arched or straight awns), 1.3-2x the length of the lemma (excluding its awn); panicle dense and spike-like, 0.8-16 cm long and 0.3-10 mm broad.
............ ......10 Culms with little to no branching above the base; internodes dull and puberulent, strigose directly below the nodes; awns of the glumes to 5 mm long; ligules 0.2-0.6 mm long
............ ......10 Culms much-branched above the base; internodes smooth, polished, and mostly glabrous (sometimes puberulent directly below the nodes); awns of the glumes to 1 mm long; ligules 0.6-1.7 mm long
............ ....9 Glumes 1.2-3 mm long, shorter than to barely exceeding the lemma; panicle usually slender, arching, generally less dense and not spike-like, often with some elongated (though appressed) branches, 4-50 cm long, 2-15 mm broad.
............ ........11 Callus glabrous; plant lacking scaly rhizomes (with slender stolons and a hard, knotty crown); leaves 0.5-2 mm wide; [calcareous cliffs]
............ ........11 Callus bearded (sometimes only slightly so) (glabrous in M. glabriflora); plant with scaly rhizomes (except for M. tenuifolia); leaves (1-) 2-14 mm wide; [various habitats].
............ ..........12 Awns of the lemma 10-30 mm long; [e. TX westward]
............ ..........12 Awns of the lemma 0.1-12 (-13) mm long; [collectively widespread]
............ ............ 13 Panicle linear, loosely flowered, much exceeding the leaves; culm erect, simple or sparingly branched; glumes relatively broad, the body ovate, 1.2-2.5 mm long, abruptly narrowed to the acuminate tip; ligule obsolete or shorter than the elongate cartilaginous summit of the leaf sheath.
............ ............ ..14 Lemmas awnless or awn < 0.5 mm long; spikelets 1.5-2.5 mm long; leaf blades usually (1-) 2-6 mm wide
............ ............ ..14 Lemma awn 1-11 mm long (rarely awnless); spikelets 3-5 mm long; leaf blades (2) 6-10 (-13) mm wide (often > 8 mm wide)
............ ............ 13 Panicle lanceolate, densely (rarely loosely) flowered, leaves often extending conspicuously into the inflorescence; culm geniculate, freely branched; glumes relatively narrow, the body lanceolate, 2-3 mm long, tapering from base to apex; ligule usually obvious above the short cartilaginous summit of the leaf sheath.
............ ............ ....15 Culm glabrous throughout (including below the nodes).
............ ............ ......16 Glumes 1.4-2.0 mm long; ligule 0.2-0.5 mm long
............ ............ ......16 Glumes 2-4 (-5) mm long; ligule 0.8-1.5 mm long
............ ............ ....15 Culm pubescent, at least below the nodes.
............ ............ ........17 Lemma awn 7-12 mm long; spikelets loosely clustered, on pedicels 2-4 mm long
............ ............ ........17 Lemma awnless or with a short awn tip (rarely to 9 mm long); spikelets densely clustered, on pedicels < 1 mm long.
............ ............ ..........18 Lemma glabrous below, or with short basal bearding; ligule 0.5-1.5 mm long
............ ............ ..........18 Lemma pilose basally; ligule 0.5-1 mm long
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