1 Spikelets tuberculate

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 6-20 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]

............ ..........12 Spikelets 1.8-3.6 mm long; panicle branches ascending-spreading at maturity.

............ ............ 13 Spikelets short-pointed to acuminate, 1.4-2.5 (-2.8) mm long; mature panicle usually 0.7-2× as long as wide.

............ ............ ..14 Sheaths glabrous except for the short-ciliate margins; culm nodes and internodes glabrous

............ ............ ..14 Sheaths hispid to villous; culm nodes usually pubescent to bearded, internodes hispid to glabrous; [Panicum section Panicum].

............ ............ ....15 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

............ ............ ....15 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.

............ ............ ......16 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]

............ ............ ......16 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].

............ ............ ........17 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

............ ............ ........17 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.

............ ............ ..........18 Plants with hard crowns, lacking rhizomes; fertile lemma 1.2-2.4 mm long.

............ ............ ............ 19 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]

............ ............ ............ 19 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

............ ............ ..........18 Plants with rhizomes; fertile lemma 1.6-4 mm long.

............ ............ ............ ..20 Rhizomes about 1 cm thick with pubescent scale-like leaves; lower portion of culm hard, nearly woody

............ ............ ............ ..20 Rhizomes less than 1 cm thick with glabrous scale-like leaves; culms not woody.

............ ............ ............ ....21 First glume truncate apically; [Panicum section Repentia]

............ ............ ............ ....21 First glume acute to obtuse.

............ ............ ............ ......22 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

............ ............ ............ ......22 Culms terete; ligules 1-6 mm long; spikelets pediceled and not at all secund, essentially straight; fertile lemma 2-4 mm long; [Panicum section Hiantes].

............ ............ ............ ........23 Panicle narrow, the branches erect; sheaths longer than internodes; spikelets 4.3-7.7 mm long; fertile lemma 3-4 mm long.

............ ............ ............ ..........24 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

............ ............ ............ ..........24 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

............ ............ ............ ........23 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.

............ ............ ............ ............ 25 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

............ ............ ............ ............ 25 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.

............ ............ ............ ............ ..26 Rhizomes short, densely interlocking, culms subascending at base, densely clumped

............ ............ ............ ............ ..26 Rhizomes elongate, or if short, then culms horizontally divergent at base, loosely clumped