1. Plants developing both subterranean and aerial inflorescences, only the subterranean spikelets setting seed | Amphicarpum |
1. Plants developing only aboveground inflorescences, the spikelets setting seed [Amphicarpum is also keyed out here to accommodate situations in which looking for subterranean inflorescences is not permitted or specimens have no underground parts]. | → 2 |
2. Inflorescences spikelike panicles, with the branches partially embedded in the flattened rachises; plants perennial, stoloniferous | Stenotaphrum |
2. Inflorescences panicles, sometimes spikelike, but the branches not embedded in the rachises or the rachises not flattened; plants annual or perennial, sometimes stoloniferous. | → 3 |
3. Most spikelets or groups of 2-11 spikelets subtended by 1-many, distinct to more or less connate, stiff bristles or bracts. | → 4 |
4. Spikelets in groups of 2-11, subtended by 4 flat, narrowly elliptic, coriaceous bracts; terete bristles not present | Anthephora |
4. Spikelets solitary or in groups, subtended by 1-many stiff, terete bristles, sometimes appearing as an extension of the branch; flat, connate bristles sometimes present distal to the terete bristles. | → 5 |
5. Bristles falling with the spikelets at maturity; disarticulation at the base of the reduced panicle branches (fascicles). | → 6 |
6. Bristles plumose or antrorsely scabrous, free or fused no more than 1/2 their length | Pennisetum |
6. Bristles glabrous, smooth, retrorsely scabrous, or strigose, usually at least some bristles fused for more than 1/2 their length | Cenchrus |
5. Bristles persistent; disarticulation below the spikelets. | → 7 |
7. Upper glumes indurate at maturity; lower lemmas somewhat indurate at the base; pedicels subtended by a single bristle | Setariopsis |
7. Upper glumes membranous to herbaceous at maturity; lower lemmas neither constricted nor indurate at the base; pedicels subtended by 1-many bristles. | → 8 |
8. Spikelets subtended by 1-many bristles; paleas of the lower florets usually hyaline to membranous at maturity, rarely absent or reduced; paleal veins not keeled | Setaria |
8. Spikelets subtended by 1 bristle; paleas of the lower florets coriaceous to indurate at maturity, the keels thickened | Ixophorus |
3. All or most spikelets not subtended by stiff bristles, sometimes the terminal spikelet on each branch subtended by a single bristle, and occasionally other spikelets with a single subtending bristle. | → 9 |
9. Terminal spikelet on each branch subtended by a single bristle; other spikelets occasionally with a single stiff subtending bristle | Setaria |
9. None of the spikelets subtended by a stiff bristle. | → 10 |
10. Inflorescences of spikelike branches 1-3.7 cm long, the branch axes extending as a 2.5-4 mm bristle beyond the base of the distal spikelets | Paspalidium |
10. Inflorescences various but, if of spikelike branches, these terminating in a well-developed or rudimentary spikelet. | → 11 |
11. Lower glumes or lower lemmas awned, sometimes shortly so (the awn reduced to a point in Echinochloa colona). | → 12 |
12. Upper florets laterally compressed; spikelets also laterally compressed | Melinis |
12. Upper florets dorsally compressed; spikelets usually dorsally compressed or terete, sometimes laterally compressed. | → 13 |
13. Blades linear to linear-lanceolate, usually more than 10 times longer than wide, with prominent midribs; at least the upper leaves, often all leaves, without ligules; ligules usually absent, particularly from the upper leaves, of hairs when present | Echinochloa |
13. Blades triangular to lanceolate, less than 10 times longer than wide, the midribs not particularly prominent, at least distally; ligules present, of hairs or membranous. | → 14 |
14. Lower glumes awned, the awns exceeding the florets; upper glumes not ciliate-margined; culms trailing on the ground, frequently rooting and branching at the nodes | Oplismenus |
14. Lower glumes unawned or shortly awned, the awns exceeded by the florets; upper glumes ciliate-margined; culms erect or decumbent below, sometimes rooting and branching at the lower nodes | Alloteropsis |
11. Lower glumes and lower lemmas unawned. | → 15 |
15. Upper florets laterally compressed | Melinis |
15. Upper florets dorsally compressed or terete. | → 16 |
16. Upper lemmas and paleas cartilaginous and flexible at maturity; lemma margins flat, hyaline; lower glumes absent or to 1/4 the length of the spikelets. | → 17 |
17. Aerial inflorescences with elongate rachises and glabrous spikelets; spikelets of the aerial panicles rarely setting seed; subterranean spikelets developed, seed-forming | Amphicarpum |
17. Aerial inflorescences of digitate or subdigitate clusters of spikelike branches with glabrous or pubescent spikelets or with elongate rachises and conspicuously pubescent spikelets; aerial spikelets seed-forming; subterranean spikelets not developed. | → 18 |
18. Spikelets ellipsoid to obovoid; inflorescences simple panicles with erect to ascending branches on elongate rachises; branches ascending, not conspicuously spikelike | Anthenantia |
18. Spikelets lanceoloid to ellipsoid; inflorescences usually panicles with digitate or subdigitate clusters of spikelike branches, sometimes simple panicles with strongly divergent branches | Digitaria |
16. Upper lemmas and paleas chartaceous to indurate and rigid at maturity; lemma margins not hyaline, frequently involute; lower glumes varying from absent to subequal to the spikelets or extending beyond the distal floret. | → 19 |
19. Spikelets subtended by a cuplike callus | Eriochloa |
19. Spikelets not subtended by a cuplike callus. | → 20 |
20. At least the upper leaves, often all leaves, without ligules; ligules, when present, of hairs | Echinochloa |
20. All leaves with ligules, ligules membranous or of hairs. | → 21 |
21. Paleas of the lower florets inflated and indurate at maturity; lower and upper florets standing apart from each other when mature | Steinchisma |
21. Paleas of the lower florets neither inflated nor indurate at maturity; lower and upper florets closely appressed to each other when mature, [revert to left side] | → 22 |
22. Inflorescences of 1-sided, spikelike primary branches. | → 23 |
23. Spikelets with the lower lemmas and lower glumes (if present) adjacent to the branch axes. | → 24 |
| Axonopus |
24. Lower glumes present on all or most spikelets. | → 25 |
25. Upper lemmas rugose and verrucose; panicle branches in 2 or more ranks, sometimes verticillate | Urochloa |
25. Upper lemmas smooth; panicle branches in 1 rank | Moorochloa |
23. Spikelets with the upper lemmas and upper glumes (if present) adjacent or appressed to the branch axes. | → 26 |
26. Both glumes absent from all or almost all spikelets, the terminal spikelet on a branch sometimes with upper glumes | Reimarochloa |
26. Upper or both glumes present on all spikelets. | → 27 |
27. Upper lemmas smooth to slightly rugose; lower glumes usually absent | Paspalum |
27. Upper lemmas rugose and verrucose; lower glumes present, from 1/5 as long as the spikelets to equaling them | Urochloa |
22. Inflorescences usually panicles with well-developed secondary branches, sometimes spikelike panicles or panicles with spikelike, but not 1-sided, branches. | → 28 |
28. Inflorescences dense, the spikelets concealing at least the distal 1/2 of the rachises. | → 29 |
29. Upper glumes slightly to strongly saccate, 5-13-veined; panicle branches often fused to the rachises; blades 1.5-22 mm wide; culm internodes hollow | Sacciolepis |
29. Upper glumes not saccate, 3-7-veined; panicle branches not fused to the rachises; blades 12-28 mm wide; culm internodes filled with aerenchyma | Hymenachne |
28. Inflorescences more or less open panicles, the spikelets not concealing the rachises. | → 30 |
30. Lower glumes with saccate bases; glumes and lemmas with woolly pubescent apices; culms weakly lignified, rooting at the nodes | Lasiacis |
30. Lower glumes not saccate basally; glumes and lemmas glabrous or with short, straight hairs, apices sometimes with a tuft of hairs but never woolly pubescent; culms usually not lignified, if lignified, not rooting at the nodes. | → 31 |
31. Lemmas of the upper florets rugose and verrucose; panicle branches usually spikelike and 1-sided, alternate or subopposite, less frequently verticillate | Urochloa |
31. Lemmas of the upper florets usually smooth, if rugose the panicle branches neither verticillate nor 1-sided and spikelike. | → 32 |
32. Plants developing aerial and subterranean panicles; aerial spikelets lanceoloid, often without lower glumes; upper lemmas with flat margins | Amphicarpum |
32. Plants developing aerial, but not subterranean, panicles; spikelets ovoid to ellipsoid or lanceoloid; lower glumes present; upper lemmas with involute margins. | → 33 |
33. Blades of the basal leaves clearly distinct from the cauline leaves; basal leaves ovate to lanceolate, cauline leaves with longer and narrower blades; basal leaves forming a distinct winter rosette | Dichanthelium |
33. Blades of the basal and cauline leaves similar, usually linear to lanceolate, varying from filiform to ovate; basal leaves not forming a distinct winter rosette. | → 34 |
34. Panicles terminating the culms usually appearing in late spring; branches usually developing from the lower and middle cauline nodes in summer, the branches rebranching 1 or more times by fall; upper florets not disarticulating at maturity, plump | Dichanthelium |
34. Panicles terminating the culms usually appearing after midsummer; branches usually not developing branches from the lower and middle cauline nodes, when present, rarely rebranched; upper florets disarticulating or not very plump at maturity | Panicum |