1 Spikelets tuberculate (or tuberculate-hispid)

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]

                                       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.

                                             22 First glume truncate apically (subacute in P. gouinii); [Panicum section Repentia].

                                               23 Panicle dense, with purplish spikelets; first glume triangular to subacute, ca. 1/3rd the length of the spikelet

                                               23 Panicle loosely flowered; first glume truncate, ca. 1/5th the length of the spikelet

                                             22 First glume acute to obtuse.

                                                 24 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].

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

                                                      26 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

                                                      26 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

                                                    25 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.

                                                        27 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

                                                        27 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.

                                                          28 Rhizomes short, densely interlocking, culms subascending at base, densely clumped

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

1 Inflorescences spikelike branches, the spikelets partially embedded in the rachises

1 Inflorescences panicles or spikes (if spikes, the spikelets not embedded.

  2 Spikelets (at least the terminal) subtended by 1-many stiff, terete bristles.

    3 Bristles persistent on the inflorescence, each spikelet disarticulating above the bristles

    3 Bristles falling with the spikelets at maturity (the disarticulation at the base of the fascicles)

  2 Spikelets not subtended by stiff bristles.

      4 Inflorescences of spikelike branches 1-3.7 cm long, the branch extending 2.5-4 mm beyond the attachment of the distal spikelets

      4 Inflorescences not as above.

        5 Upper florets laterally compressed

        5 Upper florets dorsally compressed.

          6 Fertile (upper) florets shiny and black to brown-colored when mature; the glumes abruptly apiculate and (internally) oily, the lower glume bases saccate; plants erect, arching, climbing, or decumbent; [s. FL only in our flora area]

          6 Plants not as above (if robust, lacking shiny black florets and not arching or climbing); [collectively widespread, including s. FL].

             7 Lower glumes or lower lemmas awned.

               8 Leaves > 10× as long as wide; ligules absent or of hairs

               8 Leaves < 8× as long as wide; ligules present, membranous or of hairs.

                 9 Lower glumes unawned or very shortly so; upper glumes ciliate-margined; plants erect or basally decumbent

                 9 Lower glumes awned; upper glumes not ciliate-margined; culms trailing; plants strongly trailing, rooting at the nodes

             7 Lower glumes and lower lemmas unawned.

                   10 Lemma margins flat, hyaline; lower glumes absent or < ¼ the length of the upper glume.

                     11 Subterranean (cleistogamous) inflorescences present; aerial inflorescences with elongate rachises; spikelets of the aerial inflorescences often sterile; spikelets glabrous; leaves either with a white cartilaginous margin or prominently ciliate; [of the Coastal Plain]

                     11 Subterranean inflorescences absent; aerial inflorescences either with digitate or subdigitate branches and glabrous spikelets, or with elongate rachises and conspicuously pubescent spikelets; spikelets of the aerial inflorescences fertile; spikelets glabrous, ciliate, or pubescent; leaves various (often not as above); [collectively widespread]

                       12 Inflorescence a narrow panicle with the branches strongly ascending to appressed; spikelets ellipsoid to obovoid; [of Coastal Plain pinelands]

                       12 Inflorescence either a panicle with digitate or subdigitate clusters of spikelike branches or a broad panicle with widely divergent branches; [widespread]

                   10 Lemma margins not hyaline, frequently involute; lower glumes various (absent, < ¼ the length, to longer than the upper glume).

                          13 Spikelets subtended by a cuplike callus

                          13 Spikelets not subtended by a cuplike callus.

                            14 Leaves primarily lacking ligules (at least the upper, and often all, leaves without ligules, if vestigial ligules present, these of hairs)

                            14 Leaves with ligules, these either membranous or of hairs.

                              15 Lower (sterile) palea indurate and expanding the spikelet at maturity, as long as the lower (sterile) lemma; lower and upper florets standing apart from one another at maturity; outer surface of the upper (fertile) palea with compound papillae

                              15 Lower (sterile) palea membranous, not expanding the spikelet at maturity, usually shorter than lower (sterile) lemma, or absent; lower and upper florets closely appressed at maturity; outer surface of the upper (fertile) palea lacking compound papillae.

                                16 Inflorescence of 1-sided, spikelike primary branches.

                                  17 Spikelets with lower lemmas (and lower glumes, if present) adjacent to the branch axes.

                                    18 Lower glumes absent

                                    18 Lower glumes present on at least most spikelets

                                  17 Spikelets with upper lemmas (and upper glumes, if present) adjacent or appressed to the branch axes.

                                       19 Both glumes absent from all or most spikelets

                                       19 Upper or both glumes present on all spikelets.

                                         20 Lower glumes usually absent; upper lemmas smooth to slightly rugose

                                         20 Lower glumes present; upper lemmas rugose and verrucose

                                16 Inflorescence either paniculate with well-developed secondary branchlets or if the primary branches spikelike, then the spikelets not borne in a 1-sided arrangement on the spicate branches.

                                           21 Inflorescences dense, the spikelets obscuring most of the internal branches

                                           21 Inflorescences open panicles, or if narrowed, all or nearly all the panicle branches readily visible.

                                             22 First glume 5-7.5 mm long, nearly as long as sterile lemma; fertile lemma 1/3 length of sterile lemma; rachilla prolonged between the florets

                                             22 First glume shorter, or if this long, then at most 3/4 length of sterile lemma; fertile lemma > ½ the length of the sterile lemma; rachilla not prolonged between the florets.

                                               23 Plant developing a terminal (“spring”) inflorescence usually before mid-summer, followed by lateral (“autumnal”) inflorescences from lower, mid, and/or upper nodes, these often included or hidden among the fascicles of smaller “autumnal” leaves; often developing a rosette of overwintering basal leaves

                                               23 Plant developing a terminal inflorescence usually after mid-summer, the lateral inflorescences, when present, from the upper nodes, usually appearing at the same time as the terminal panicle, and not hidden by dense fascicles of smaller leaves; plants lacking a rosette of overwintering basal leaves.

                                                 24 Spikelets tuberculate (or tuberculate-hispid)

                                                 24 Spikelets smooth, not tuberculate.

                                                    25 Panicle < 2 cm wide at maturity.

                                                      26 Spikelets > 4.5 mm long; first glume > 2.4 mm long; ligule 4-6 mm long; [of coastal dunes]

                                                      26 Spikelets < 4 mm long; first glume < 2.1 mm long; ligule < 2 mm long; [not of coastal dunes].

                                                        27 Blades flat, the larger 6-20 mm wide; culms stout.

                                                          28 Panicles constricted, 0.3-1.6 cm wide; spikelets subsessile to short-pediceled; summit of fertile palea not enclosed by fertile lemma

                                                    25 Panicle > 2 cm wide at maturity.

                                                            29 Fertile lemmas rugose with cross-venation between the main parallel veins

                                                            29 Fertile lemmas not rugose.

                                                              30 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

                                                              30 Plants without the above combination of characters.

                                                                 31 Plants from a cluster of fibrous roots, without rhizomes or hard knotty crowns, annual

                                                                 31 Plants with rhizomes or hard knotty crowns, perennial.

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

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

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

                                                                       34 First glume truncate apically

                                                                       34 First glume acute to obtuse.

                                                                         35 Culms terete; ligules 1-6 mm long; at least some spikelet pedicels spreading, spikelets not at all secund, essentially straight; fertile lemma 2-4 mm long