1 Inflorescences dense and spikelike, symmetrical, cylindrical or ovoid, unbranched; [genus Crypsis, or if treated as part of Sporobolus, section Crypsis; subsection Crypsis]

..2 Plant annual; spikelike panicle 0.3-7.5 cm long

..2 Plant perennial; spikelike panicle (10-) 15-45 (-50) cm long

1 Inflorescences loose and open, or if relatively dense, then with discernible branches, and thus lobed or asymmetrical.

....3 Inflorescence a slender or broad panicle.

......4 Florets with a conspicuous tuft of hairs on the callus; [genus Calamovilfa, or, if treated as part of Sporobolus, section Calamovilfa; subsection Calamovilfa].

......4 Florets not conspicuously hairy on the callus.

........5 Inflorescence a contracted, (superficially) spike-like panicle, < 6 cm broad, the branches appressed to strongly ascending.

..........6 Inflorescence 2-5 cm long; most inflorescences enclosed by sheaths (or most or all exserted); plant a geniculate annual; [section Clandestini].

............ 7 Spikelets (1.3-) 1.6-2.8 mm long; grain falling free of the lemma and palea; lemma glabrous

............ 7 Spikelets 2.3-5 mm long; grain falling enclosed in the lemma and palea; lemma strigose (use 10× or more magnification) or glabrous.

............ ..8 Lemma and palea shorter than the glumes; palea usually shorter than the lemma; lemma glabrous or strigose with hairs < 0.2 mm long; spikelets 2.3 -3.3 (-3.8) mm long; floret (lemma, palea and enclosed grain) 1.6-3.3 (-3.8)× as long as wide

............ ..8 Lemma and palea longer than the glumes; palea usually longer than the lemma; lemma strigose with hairs > 0.2 mm long; spikelets 2.8-5 mm long; floret (lemma, palea and enclosed grain) 2.2-5.7 (-7.5)× as long as wide

..........6 Inflorescence 4-15 cm long; most inflorescences exserted to partly enclosed; plant a rhizomatous or tufted perennial or cespitose annual.

............ ....9 Plant creeping extensively by slender rhizomes; leaf blades cauline, distichous, to 12 cm long; [section Virginicae]

............ ....9 Plant loosely tufted, from short rhizomes; leaf blades basal or cauline, not distichous, 10-100 cm long.

............ ......10 Spikelets 1.2-2.2 mm long; first glume 0.5-0.8 mm long; leaves primarily basal; [section Sporobolus].

............ ........11 Panicle branches appressed, 0.5-2 cm long in the middle of the inflorescence; second glume acute, > ½ as long as the spikelet

............ ........11 Panicle branches strongly ascending, 2-8 cm long in the middle of the inflorescence; second glume truncate or broadly obtuse, < ½ as long as the spikelet.

............ ..........12 Plants to 7.5 dm tall; leaf blades to 4 dm long and 2.5-3.5 mm wide

............ ..........12 Plants to 17 dm tall; leaf blades to 7 dm long and 6-8 mm wide

............ ......10 Spikelets 4-8 mm long; first glume 2-5 mm long; leaves cauline and basal; [section Clandestini].

............ ............ 13 Lemma pubescent, usually conspicuously shorter than the palea; pericarp loose when moist

............ ............ 13 Lemma glabrous, about as long as the palea; pericarp gelatinous when moist.

............ ............ ..14 Culms (1.4-) 2.0-5.0 mm thick; uppermost leaf sheath (1.3-) 1.5-6.0 mm wide near its base; panicles with 12-35 primary branches, crowded, densely flowered

............ ............ ..14 Culms 1.0-2.0 (-2.5) mm thick; terminal sheath 0.8-2.0 (-2.5) mm wide near its base; panicles with 8-18 primary branches, lax, loosely flowered.

............ ............ ....15 Plants cespitose, lacking scaly rhizomes

............ ............ ....15 Plants forming clonal patches, with scaly rhizomes

........5 Inflorescence an open panicle, > 2 cm broad, the branches ascending to spreading.

............ ............ ......16 Branches of the panicle verticillate, whorled; spikelets 2.5-4 mm long; [section Triachyrum]

............ ............ ......16 Branches of the panicle alternate (some occasionally rather randomly subopposite or opposite, but never regularly whorled); spikelets either 4-6.5 mm long, or 1.2-3.0 mm long.

............ ............ ........17 Spikelets 1.2-3.0 mm long.

............ ............ ..........18 Flag blades (the last leaf below the panicle) nearly perpendicular to the culm; sheath apices with a tuft of white hairs; [section Cryptandri]

............ ............ ..........18 Flag blades ascending to appressed; sheath apices glabrous or with few and scattered hairs.

............ ............ ............ 19 Mature panicle (1-) 2-5 cm wide; [section Pyramidati].

............ ............ ............ ..20 Primary panicle branches bearing spikelets to the base

............ ............ ............ ..20 Primary panicle branches without spikelets in the lower 1/8 to ½ of their length

............ ............ ............ 19 Mature panicle 12-35 cm wide; [section Airoides]

............ ............ ............ ....21 Secondary panicle branches bearing spikelets throughout their length; pedicels mostly spreading, mostly 0.2-0.5 mm long; [section Airoides]

............ ............ ............ ....21 Secondary panicle branches bearing spikelets only in the upper 3/4 or 1/2 of their length; pedicels appressed, mostly 0.5-25 mm long.

............ ............ ............ ......22 Pedicels 0.5-2 mm long; anthers 1.1-1.8 mm long; [section Airoides]

............ ............ ............ ......22 Pedicels 6-25 mm long; anthers 0.3-1.0 mm long; [section Cryptandri]

............ ............ ........17 Spikelets 4-6.5 mm long; [section Calamovilfa; subsection Floridani].

............ ............ ............ ........23 First glume scaberulous, acuminate or awn-like; spikelets dark gray; base of plant relatively fibrous; grain spherical; [of barrens and prairies of IN, IL, MO, and n. AR, scattered eastwards as a disjunct, almost always inland of the Coastal Plain]

............ ............ ............ ........23 First glume glabrous, acute to acuminate; spikelets purplish (fading tan); base of plant smooth and hard, made up of the indurated leaf bases; grain oblong (when present, usually abortive); [of pine savannas and seeps of the Coastal Plain of NC south to c. FL, west to e. TX and se. OK].

............ ............ ............ ..........24 Leaves terete or subterete (wiry), oval in cross-section, sometimes irregularly channeled for part of their length (never with any portion above the sheath flat), < 1 mm wide, tending to senesce and turn tan in autumn, the margins generally smooth; culms (including the inflorescence) (2-) 4-7 (-10) dm tall; culms (from base to first inflorescence branch) 1.5-5 dm tall; first glume averaging about 0.7× as long as the second glume (though variable, ranging from 0.5-0.75×)

............ ............ ............ ..........24 Leaves flat (sometimes inrolled or folded when dry), plane or v-shaped in cross-section, with free margins their entire length, (0.5-) 1.2-10 mm wide, tending to remain green into the winter (at least until December), the margins at least partially scabrous (except in S. curtissii); culms (including the inflorescence) 3-22 dm tall; culms (from base to first inflorescence branch) (4-) 6-10 dm tall; first glume averaging 0.75-1× as long as the second glume (though variable, collectively ranging from about 0.5-1.2×).

............ ............ ............ ............ 25 First glume averaging 0.95-1.1× as long as the second glume (though variable, ranging from 0.8-1.3×); pedicels mostly 1-3 mm long (a few sometimes as long as 10 mm long), strongly appressed to the panicle branches; culms (including the inflorescence) 3-7 dm tall; inflorescence branches stiffly ascending; leaves 0.5-1.5 mm wide (or to 2.0 mm wide when unburned), mostly 1.5-4 dm long (rarely to 5 dm long), smooth on the margins; [of e. SC southward and westward to s. AL]

............ ............ ............ ............ 25 First glume averaging 0.5-0.9× as long as the second glume (though variable, ranging from 0.5-0.95×); pedicels mostly 4-15 mm long, ascending to spreading; culms (including the inflorescence) (3-) 7-16 (-22) dm tall; inflorescence branches initially ascending, later loosely ascending to spreading; leaves 1.2-10 mm wide, mostly (3-) 4-8 dm long, upwardly scabridulous on at least the lower leaf margins; [e. NC southward and westward to se. OK and e. TX].

............ ............ ............ ............ ..26 Pedicels appressed; lemmas 4.4-6.5 mm long; anthers 3.5-5.0 mm long; [w. LA west to se. OK and e. TX]

............ ............ ............ ............ ..26 Pedicels spreading; lemmas 3.0-4.3 mm long; anthers 2.0-3.4 mm long; [se. NC south to c. FL, west to se. AL and FL Panhandle].

............ ............ ............ ............ ....27 Leaves (2.0-) 3-10 mm wide, typically pale bluish-green (sometimes with some yellowish leaves as well), typically widely spreading to recumbent with age; first glume averaging 0.75-0.9× as long as the second glume

............ ............ ............ ............ ....27 Leaves 1.2-3.0 (-4.0) mm wide, yellowish-green to dark green, mostly strictly ascending; first glume averaging (0.5-) 0.6-0.8× as long as the second glume.

............ ............ ............ ............ ......28 Leaves 2.0-3.0 (-4.0), yellowish-green, generally flat or folded; culms (including the inflorescence) usually (10-) 12-16 dm tall; inflorescence usually 3.5-6 dm long; pedicels glabrous or nearly so; [ne. to c. peninsular FL]

............ ............ ............ ............ ......28 Leaves 1.2-2.0 (-3.0) mm wide, dark green, often inrolled above when dry; culms (including the inflorescence) usually 6-12 (-18) dm tall; inflorescence usually 2-3.5 dm long; pedicels often scabridulous; [e. NC, SC, and e. GA]

1 Inflorescence otherwise, either the spikelets embedded or in grooves in an thickened rachis, or the inflorescence a slender or broad panicle.

..2 Spikelets embedded in the thickened rachis (the inflorescence thus like an ear of corn), or fitting into grooves in the thickened rachis (the inflorescence thus cylindrical and resembling a rat's tail). Spikelets unisexual, with male and female spikelets in separate inflorescences or in different parts of the same inflorescence; [tribe Andropogoneae].

....3 Racemes of mixed sex (female below, male above)

....3 Racemes of single sex

..2 Spikelets not embedded or fitting into grooves in the rachis, the inflorescence a slender or broad panicle (the spikelets visibly separate and often pedicelled).

......4 Spikelets with a single floret, this unisexual (either pistillate or staminate); plants with aerenchymatous culms, [plants of seasonally or tidally flooded wetlands]; [tribe Oryzeae].

........5 Pistillate spikelets on the upper branches of the panicle, staminate spikelets on the lower branches; lemmas and paleas clasping along their margins; plants annual

........5 Pistillate and staminate spikelets intermingled on the same branches of the inflorescence; lemma margins free; plants perennial

......4 Spikelets with 2 or more florets, at least some of these bisexual; plants without aerenchymatous culms, [plants of uplands or temporarily to seasonally flooded wetlands].

..........6 Spikelets with 2-8 florets, these bisexual.

............ 7 Leaves primarily basal, plants densely cespitose.

............ ..8 ; [tribe Arundineae

............ ..8 Panicles plumose; [tribe Danthonieae]

............ 7 Leaves cauline; plants short-rhizomatous (somewhat clumped) to long-rhizomatous; [tribe Arundineae].

............ ....9 Lemmas pilose; rachilla glabrous; plants short-rhizomatous (somewhat clumped); culms to 10 m tall; [plants of uplands or saturated or temporarily flooded wetlands]

............ ....9 Lemmas glabrous; rachilla sericeous; plants long rhizomatous; culms to 4 m tall; [plants of uplands or saturated, tidally flooded, or seasonally flooded wetlands]

..........6 Spikelets almost always with 2 florets, the lower florets sterile or staminate (sometimes reduced to lemmas or completely absent).

............ ......10 Spikelets falling separately, not attached to rachis segments, stalks, or bristles; spikelets <2× as long as wide; [tribe Paniceae].

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

............ ........11 Spikelets not subtended by stiff bristles.

............ ..........12 Fertile lemma rugose with cross-venation

............ ..........12 Fertile lemma smooth or hairy, not rugose

............ ......10 Spikelets falling with attached rachis segments, stalks, or bristles; spikelets >3× as long as wide; [tribe Andropogoneae].

............ ............ 13 Pedicelled spikelet differing from the sessile in shape and sex (sometimes represented only by a pedicel).

............ ............ ..14 Inflorescence of 2-13 digitate (whorled) racemes borne at the summit of a peduncle, the peduncle subtended by a raceme sheath

............ ............ ..14 Inflorescence a panicle, the branches not subtended by sheaths.

............ ............ ....15 Pedicelled spikelet represented by pedicel only; apex of sheath bearing 2 auricles 1-10 mm long; [native]

............ ............ ....15 Pedicelled spikelet present, staminate; apex of sheath truncate; [exotic]

............ ............ 13 Pedicelled spikelet similar to the sessile spikelet, both fertile.

............ ............ ......16 Spikelets falling separately from the persistent rachis

............ ............ ......16 Spikelets falling in pairs together with sections of the disarticulating rachis

............ ............ ........17 Spikelets awned with awns 10-26 mm long; anthers 2; [native, collectively common and widespread]

............ ............ ........17 Spikelets unawned or with awns to 5.2 mm long; anthers 3; [exotic, rarely encountered]

............ ............ ..........18 Spikelets unawned

............ ............ ..........18 Spikelets with awns 4-5.2 mm long

1 Spikelets 2-flowered, often dorsally compressed, falling entire at maturity (the abscission below the glumes), the upper floret usually bisexual, the lower one male or sterile; [tribe Paniceae]

..2 Lemma margins hyaline, flat; lower glumes various (absent, < ¼ the length, or longer than the upper glume)

..2 Lemma margins not hyaline, frequently involute; lower glumes absent or < ¼ the length of the upper glume.

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

......4 Lower glumes absent

......4 Lower glumes present on at least most spikelets

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

........5 Both glumes absent from all or most spikelets

........5 Upper or both glumes present on all spikelets.

..........6 Lower glumes usually absent; upper lemmas smooth to slightly rugose

..........6 Lower glumes present; upper lemmas rugose and verrucose

1 Spikelets 1-, 2-, or many-flowered, usually terete or somewhat laterally compressed, either abscising at maturing above the glumes or if 2-flowered then both florets bisexual, or the upper sterile; [tribes Cynodonteae and Zoysieae]

............ 7 Spikes normally solitary (rarely 2), divergent at the summit of the culm; second glume with a recurved spine arising from the back; fresh plants aromatic with a citrus odor; [tribe Cynodonteae; subtribe “incertae sedis”]

............ 7 Spikes normally 2 or more, alternate, digitate, subdigitate, or verticillate along the main inflorescence axis; second glume lacking a recurved spine; fresh plants not aromatic with a citrus odor.

............ ..8 Spikes arranged along the central inflorescence axis alternately, solitary at each node.

............ ....9 Spikelets with 1 bisexual floret, sometimes also with modified male, sterile, or rudimentary florets above the fertile floret.

............ ......10 Spikelets with modified male, sterile, or rudimentary florets above the fertile floret; [plants of uplands]; [tribe Cynodonteae; subtribe Boutelouinae]

............ ....9 Spikelets with 2 or more bisexual florets (sometimes also with additional reduced florets); [tribe Cynodonteae; subtribe Eleusininae].

............ ........11 Ligules 4-8 (-15) mm long, acute to attenuate, entire (lacerate only by tearing)

............ ........11 Ligules 0.3-5.4 mm long, truncate to obtuse, erose or entire.

............ ..........12 Lemmas 3-veined; ligule (0.2-) 0.5-5.5 (-7.0) mm long; apex erose or entire

............ ..........12 Lemmas 5-veined; ligule 0.8-2.2 mm long, apex erose

............ ..8 Spikes arranged along the central inflorescence axis in a digitate, subdigitate, or verticillate manner, all or most nodes with 2 or more spikes; [tribe Cynodonteae].

............ ............ 13 Spikelets with 1 fertile floret (there may also be 1 or more sterile florets); [tribe Cynodonteae; subtribe Eleusininae].

............ ............ ..14 Spikelets lacking sterile florets

............ ............ ..14 Spikelets with 1 or more sterile florets.

............ ............ ....15 Lowest lemmas awned (rarely unawned); upper glumes acute to acuminate, mucronate or short-awned

............ ............ ....15 Lowest lemmas unawned (or with an awn to 1.2 mm long); upper glumes truncate or bilobed, sometimes short-awned from between the lobes

............ ............ 13 Spikelets with 2 or more fertile florets.

............ ............ ......16 Spikes to 7 cm long, terminating in a point (the spikes acuminate); [tribe Cynodonteae; subtribe “incertae sedis”]

............ ............ ......16 Spikes to 22 cm long, terminating in a functional or rudimentary spikelet (the spikes acute to obtuse); [tribe Cynodonteae; subtribe Eleusininae].

............ ............ ........17 Lemmas glabrous

............ ............ ........17 Lemmas pubescent, at least towards the base.

............ ............ ..........18 Lemma apices obtuse to truncate or emarginate

............ ............ ..........18 Lemma apices acute