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Key to Panicum

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1 Spikelets smooth, not tuberculate.
..2 Panicle < 2 cm wide at maturity.
....3 Spikelets > 4.5 mm long; first glume > 2.4 mm long; ligule 4-6 mm long; [of coastal dunes]; [Panicum section Hiantes]
....3 Spikelets < 4 mm long; first glume < 2.1 mm long; ligule < 2 mm long; [not of coastal dunes].
......4 Blades involute, 1.5-4 mm wide; culms wiry
......4 Blades flat, the larger 2-20 mm wide; culms stout.
........5 Panicles constricted, 0.3-1.6 cm wide; spikelets subsessile to short-pediceled; summit of fertile palea not enclosed by fertile lemma
........5 Panicles > 1 cm wide; spikelets short to long-pediceled; summit of fertile palea enclosed by fertile lemma
..2 Panicle > 2 cm wide at maturity.
..........6 Lower primary panicle branches in whorls of 4-7 at the nodes, stiffly spreading, naked on the proximal ½, the axils strongly pilose; lower culm internodes appressed papillose-pubescent; first glume acuminate, ½ as long as spikelet; fertile lemma chestnut brown at maturity; [Panicum section Panicum]
..........6 Plants without the above combination of characters.
............ 7 Plants from a cluster of fibrous roots, without rhizomes or hard knotty crowns, annuals or perennials.
............ ..8 First glume 1/5 to 1/3 length of spikelet, blunt to broadly rounded to truncate; sheaths usually glabrous (papillose-hispid in P. dichotomiflorum var. bartowense); nodes glabrous; [Panicum section Dichotomiflora].
............ ....9 Plants perennial, aquatic and often floating, rooting at the lower nodes; leaf blades 2-15 mm wide.
............ ....9 Plants annual, terrestrial; leaf blades 3-25 mm wide.
............ ......10 Spikelets ovoid to slenderly ellipsoid, 1.6-2.3 mm long, widest at middle with acute tips, second glume and sterile lemma thin, submembraneous; some to many pedicels > 3 mm long and longer than spikelets; culms to 6 dm long; leaf blades 1-8 mm wide
............ ......10 Spikelets oblong-lanceolate, (2.0-) 2.4-3.6 mm long, widest below middle, tapering to acuminate tips, second glume and sterile lemma firm, subcoriaceous; most pedicels < 3 mm long and shorter than spikelets; culms to 20 dm long; leaf blades 4-20 mm wide.
............ ........11 Sheaths conspicuously papillose-hispid; ligule 1.5-3 mm long; mature plant stout, erect, usually 10-20 dm long; spikelets 2.3-2.8 mm long
............ ........11 Sheaths glabrous to sparsely pilose, the hairs not papillose-based; ligule 1-2 mm long; mature plant usually spreading to ascending, 5-10 (20) dm long; spikelets 2.3-3.8 mm long
............ ..8 First glume 1/3 to 1/2 length of spikelet, acute to subacute; sheaths villous or hispid (except in the locally introduced P. bisulcatum); nodes often bearded.
............ ..........12 Spikelets 4.5-6 mm long; panicle branches often nodding or drooping at maturity; [Panicum section Panicum].
............ ............ 13 Mature upper florets tan to orangish, not disarticulating; culms 2-12 dm tall; panicles usually nodding, not fully exserted, > 2× as long as wide; panicle branches ascending to appressed; pulvini well-developed
............ ............ 13 Mature upper florets blackish, disarticulating at maturity; culms 7-21 dm tall; panicles erect, exserted at maturity, about 2× as long as wide; panicle branches ascending to spreading; pulvini well-developed
............ ..........12 Spikelets 1.8-3.6 mm long; panicle branches ascending-spreading at maturity.
............ ............ ..14 Spikelets long-acuminate, (2.6-) 3.0-3.6 mm long; mature panicle slender, usually 2-3× as long as wide; [Panicum section Panicum]
............ ............ ..14 Spikelets short-pointed to acuminate, 1.4-2.5 (-2.8) mm long; mature panicle usually 0.7-2× as long as wide.
............ ............ ....15 Sheaths glabrous except for the short-ciliate margins; culm nodes and internodes glabrous
............ ............ ....15 Sheaths hispid to villous; culm nodes usually pubescent to bearded, internodes hispid to glabrous; [Panicum section Panicum].
............ ............ ......16 Panicle usually equal to or longer than portion of culm below panicle, often basally included at maturity; panicle rachis, branches, and pedicels usually scabrous with barbs > 0.05 mm; pulvini usually pilose to villous, especially at lower primary branches (sometimes glabrous); culm usually not obviously zig-zag; larger blades usually more than 10 mm wide; spikelets 1.6-2.9 (-4) mm long, short- to long-acuminate, lanceolate, lance-ovoid, or lance-ellipsoid; first glume 0.6-1.5 (-2) mm long
............ ............ ......16 Panicle usually not as long as portion of culm below panicle, usually exerted at maturity; panicle rachis and branches usually smooth, the pedicels often scabrous with barbs < 0.05 mm; pulvini glabrous to sparsely (-moderately) pilose; culm often zig-zag at least proximally; larger blades usually no more than 4-12 mm wide; spikelets 1.4-2.4 mm long, pointed to short-acuminate, lance-ellipsoid, ellipsoid, ovoid, or obovoid; first glume 0.4-0.9 (-1.2) mm long.
............ ............ ........17 Herbage usually purple-tinged (-yellowish-green); internodes glabrous to sparsely hispid; blades 2-6 mm wide, ascending; pulvini glabrous to sparsely pilose; spikelets 1.8-2.2 mm long, twice or more as long as wide; mature fertile lemma blackish (rarely stramineous); [plants of granite outcrops of NC, SC, and GA]
............ ............ ........17 Herbage yellow-green to green or purple-tinged; internodes glabrate to densely hispid; blades 2-12 mm wide, spreading to ascending; pulvini glabrous to pilose; spikelets 1.4-2.4 mm long, < 2 to 2 × as long as wide; mature fertile lemma stramineous to blackish; [plants of a variety of open or wooded, dry or wet, and often disturbed sites].
............ ............ ..........18 Culms to 1 m long; internodes sparsely to densely hispid; blades to 12 mm wide; blade of flag (inflorescence bract) usually > ½ as long as panicle; panicle ellipsoid to obovoid, moderately to densely flowered; pulvini glabrous to sparsely pilose; spikelets 1.7-2.4 mm long
............ ............ ..........18 Culms to 0.5 m long; internodes glabrate to hispid; blades to 6 mm wide; blade of flag (inflorescence bract) usually < ½ as long as panicle; panicle ovoid to deltoid, sparingly to moderately flowered; pulvini sparsely to moderately pilose; spikelets 1.4-2.2 (-2.4) mm long
............ 7 Plants with rhizomes or hard knotty crowns, perennial.
............ ............ ............ 19 Plants with hard crowns, lacking rhizomes; fertile lemma 1.2-2.4 mm long.
............ ............ ............ ..20 Nodes sericeous, pilose, or glabrous; internodes often glaucous; spikelets usually appressed but not secund; pedicels 1-15 mm long; second glumes and sterile lemmas 7-11-veined; fertile lemmas 0.7-1.2 mm wide; [Panicum section Panicum]
............ ............ ............ ..20 Nodes glabrous; internodes not glaucous; spikelets appressed, usually secund; pedicels 0.5-1.5 mm long; second glumes and sterile lemmas 5-veined; fertile lemmas 0.6-0.8 mm wide
............ ............ ............ 19 Plants with rhizomes; fertile lemma 1.6-4 mm long.
............ ............ ............ ....21 Rhizomes about 1 cm thick with pubescent scale-like leaves; lower portion of culm hard, nearly woody
............ ............ ............ ....21 Rhizomes less than 1 cm thick with glabrous scale-like leaves; culms not woody.
............ ............ ............ ........23 Culms slightly compressed below; ligules 0.5 mm long or less; spikelets subsessile and subsecund, usually some obliquely bent above the first glume; fertile lemma 1.8-2.2 mm long
............ ............ ............ ........23 Culms terete; ligules 1-6 mm long; spikelets pedicelled and not at all secund, essentially straight; fertile lemma 2-4 mm long; [Panicum section Hiantes].
............ ............ ............ ..........24 Panicle narrow, the branches erect; sheaths longer than internodes; spikelets 4.3-7.7 mm long; fertile lemma 3-4 mm long.
............ ............ ............ ............ 25 First glumes 2.5-5.5 mm long, 2/3-3/4 as long as the spikelet, 7-9 nerved, the nerves thickened and raised; rhizomes usually elongate; culms solitary to loosely tufted, 0.2-1.5 m tall; leaves 0.7-3.6 dm long; panicles 2-6 cm wide, the primary branches usually 1-2 per node, loosely flowered; spikelets 4.7-7.7 mm long; fertile lemma 1.3-1.8 mm wide
............ ............ ............ ............ 25 First glumes 2-3.5 mm long, 1/2-2/3 as long as the spikelet, 3-5 (-7) nerved, the nerves thin and wiry; rhizomes usually short; culms usually tufted, 1-2 (-3) m tall; leaves 2-5 dm long; panicles 3-10 cm wide, the primary branches usually 2 or more per node, densely flowered; spikelets 4.0-5.9 mm long; fertile lemma 1.0-1.5 mm wide
............ ............ ............ ..........24 Panicle with divergent to spreading-ascending branches; upper sheaths shorter than internodes; spikelets 2.8-5 mm long; fertile lemma 2-2.6 mm long.
............ ............ ............ ............ ..26 Spikelets 2.8-3.5 mm long; beak of sterile lemma exceeding fertile lemma by 0.2-0.5 mm; first glume (blunt-) acute, ½-2/3× as long as spikelet
............ ............ ............ ............ ..26 Spikelets 3.2-5 mm long; beak of sterile lemma exceeding fertile lemma by 0.6-1.3 mm; first glume acuminate, 3/5-3/4× as long as spikelet.
............ ............ ............ ............ ....27 Rhizomes short, densely interlocking, culms subascending at base, densely clumped
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