Poaceae tribe Paniceae
Pennisetum
fountain grass
3-800 cm, annual, usually not woody.
3-800 cm, not woody, sometimes branching above the base;
internodes solid or hollow.
basal and/or cauline;
sheaths usually open;
ligules of hairs or membranous, membranous ligules often ciliate, cilia sometimes longer than the membranous base;
blades occasionally pseudopetiolate, seldom disarticulating at maturity.
terminal, sometimes also axillary, occasionally subterranean panicles;
branches sometimes spikelike and secund, sometimes less than 1 cm;
disarticulation usually below the glumes, sometimes at the base of the panicle branches, occasionally below the florets.
spicate panicles with highly reduced branches termed fascicles;
panicles 1-many per plant, terminal on the culms or on both the culms and the secondary branches, or terminal and axillary, or only axillary, usually completely exposed at maturity;
rachises usually terete, with (1)5-many fascicles;
fascicle axes 0.2-7.5(28) mm, with (1)3-130+ bristles and 1-12 spikelets.
usually dorsally compressed, varying to terete or laterally compressed, with 2(3) florets, lower florets staminate, sterile, or reduced, upper florets usually bisexual;
calluses not developed.
with 2 florets;
lower glumes absent or present, 0-5-veined;
upper glumes longer, 0-11-veined;
lower florets sterile or staminate;
lower lemmas usually as long as the spikelets, membranous, 3-15-veined, margins usually glabrous;
lower paleas present or absent;
upper lemmas membranous to coriaceous, 5-12-veined;
upper paleas shorter than the lemmas but similar in texture;
lodicules 0 or 2, glabrous;
anthers 3, if present, x = 5,7, 8,9 (usually 9).
usually membranous;
lower glumes usually less than 1/2 as long as the spikelets, sometimes absent;
upper glumes usually subequal to the upper florets, occasionally absent;
lower lemmas similar to the upper glumes in length and texture;
upper lemmas indurate, coriaceous, or cartilaginous, with a germination flap at the base, margins usually widely separated and involute at maturity, sometimes flat and hyaline;
upper paleas similar to the upper lemmas in length and texture;
lodicules short;
anthers usually 3;
stigmas usually red.
usually dorsally compressed or terete;
embryos 1/2 or more the length of the caryopses.
membranous and ciliate, or of hairs, rarely completely membranous;
blades sometimes pseudopetiolate.
free or fused at the base, disarticulating with the spikelets at maturity; of 3 kinds, outer, inner, and primary, in some species with all 3 kinds present below each spikelet, in others 1 or more kinds missing from some or all of the spikelets;
outer (lower) bristles antrorsely scabrous, terete;
inner (upper) bristles antrorsely scabrous or long-ciliate, usually flatter and wider than the outer bristles;
primary (terminal) bristles located immediately below the spikelets, solitary, antrorsely scabrous or long-ciliate, often longer than the other bristles associated with the spikelet;
disarticulation usually at the base of the fascicles, sometimes also beneath the upper florets.
= 9, 10.
Poaceae tribe Paniceae
Pennisetum
The tribe Paniceae, which includes about 100 genera and 2000 species, is primarily tropical in distribution. Within the Flora region, it is represented by 27 genera and 262 species, with its greatest representation being in the eastern portion of the contiguous United States (Barkworth and Capels 2000).
The tribe is so morphologically distinct that it was first recognized, in essentially its current sense, by Robert Brown in 1814. Its primary distinguishing features are the unusual spikelet structure combined with the indurate to coriaceous upper florets. Recent molecular studies (Barber et al. 2002; Guissani et al. 2001) show it as comprising two distinct lineages, one of which contains species with a base number of x = 9 and the other, species with x = 10.
Photosynthesis in the Paniceae may follow the C3 pathway or any of three different C4 pathways. Most genera are uniform in this regard, but there are some noteworthy exceptions. Guissani et al. (2001) concluded that the C3 pathway is probably ancestral within the tribe and that two of the three C4 pathways, NAD-ME and PCK, originated only once within the tribe, whereas the NADP-ME pathway originated independently in several different lineages. Most genera are uniform with respect to their photosyntheticd pathway, but there are some noteworthy exceptions.
The germination flap is a small area of soft tissue at the base of the upper lemma through which the primary root of the seedling grows.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Pennisetum has 80-130 species, most of which grow in the tropics and subtropics, and occupy a wide range of habitats. Twenty-five species are native to the Western Hemisphere, but none to the Flora region. Most of the species treated here are cultivated for food, forage, or as ornamental plants. Many species, including several cultivated species, are weedy. Four are classified as noxious weeds by the U.S. Department of Agriculture. Records known to be based on cultivated plants are not included in the distribution maps but, in many cases, it is not possible to determine whether a record is based on a cultivated plant or an escape.
The placement of the boundary between Pennisetum and Cenchrus is contentious. As treated here, Pennisetum has antrorsely scabrous bristles that are not spiny, fascicle axes that terminate in a bristle, and chromosome base numbers of 5, 7, 8, and 9. Cenchrus has retrorsely (rarely antrorsely) scabrous, spiny bristles, fascicle axes that are terminated by a spikelet, and a chromosome base number of 17 (Wipff 2001). In both genera, the bristles are reduced branches (Goebel 1882; Sohns 1955).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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 |
24. Lower glumes absent | 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 |
1. Plants stoloniferous; panicles axillary, partially or wholly hidden in the leaf sheaths at maturity, the rachises flattened in cross section, with 1-6 fascicles; spikelets 10-22 mm long, bristles mostly shorter than the spikelet | P. clandestinum |
1. Plants not stoloniferous; panicles terminal or terminal and axillary, fully exserted at maturity, the rachises terete, with 10-many fascicles; spikelets 2.5-12 mm long, the majority of the bristles as long as or longer than the spikelets. | → 2 |
2. Fascicles with only 1 bristle and 1 spikelet | P. petiolare |
2. Fascicles with 6 or more bristles and 1-12 spikelets. | → 3 |
3. Most or all bristles scabrous, the primary bristles sometimes sparsely and inconspicuously long-ciliate. | → 4 |
4. Primary bristles not noticeably longer than all the other bristles in the fascicles. | → 5 |
5. Terminal panicle erect; fascicles with a stipelike base 1.5-5.6 mm long | P. alopecuroides |
5. Terminal panicle drooping; fascicles subsessile, the bases 0.4-0.7 mm long. | → 6 |
6. Plants green; most of the bristles only slightly longer than the spikelets; upper glumes (7)9-veined, about as long as the spikelets | P. nervosum |
6. Plants purplish; bristles at least twice as long as the spikelets; upper glumes 1-3-veined, usually about 1/2 as long as the spikelets | P. macrostachys |
4. Primary bristles noticeably longer than all the other bristles in the fascicles. | → 7 |
7. Panicles dense; rachises with 21-40 fascicles per cm. | → 8 |
8. Rachises pubescent; bristles yellow or purple; leaf blades (4)12-40 mm wide; paleas of lower florets present | P. purpureum |
8. Rachises scabrous; bristles white to stramineous; leaf blades 4-12 mm wide; paleas of lower florets absent | P. macrourum |
7. Panicles less dense; rachises with 5-16 fascicles per cm. | → 9 |
9. Panicles drooping, terminal and axillary; leaf blades 19-45 mm wide | P. latifolium |
9. Panicles erect, all terminal; leaf blades 2-12 mm wide. | → 10 |
10. Plants not rhizomatous; lower part of rachises pubescent | P. alopecuroides |
10. Plants rhizomatous; lower part of rachises scabrous | P. flaccidum |
3. Bristles, at least the primary bristles, conspicuously long-ciliate. | → 11 |
11. Spikelets 9-12 mm long | P. villosum |
11. Spikelets 2.5-7 mm long. | → 12 |
12. Fascicles not disarticulating from the rachises; panicles 4-200 cm long; upper lemmas with pubescent margins; caryopses protruding from the florets at maturity | P. glaucum |
12. Fascicles disarticulating from the rachises at maturity; panicles 2-37.5 cm long; upper lemmas with glabrous margins; caryopses concealed by the lemmas and paleas at maturity. | → 13 |
13. Upper florets readily disarticulating at maturity; upper lemmas smooth and shiny, conspicuously different in texture from the lower lemmas. | → 14 |
14. Fascicles with 6-14 long-ciliate inner bristles and 13-30 scabrous outer bristles; fascicle axes 0.2-0.5 mm long; spikelets sessile | P. polystachion |
14. Fascicles with 40-90 long-ciliate inner bristles and 10-20 scabrous outer bristles; fascicle axes 1.5-2.5 mm long; spikelets pedicellate, the pedicels 1-3.5 mm long | P. pedicellatum |
13. Upper florets not disarticulating at maturity; lower and upper lemmas similar in texture. | → 15 |
15. Lower portion of the rachises glabrous, sometimes scabrous. | → 16 |
16. Inner bristles neither grooved nor fused, even at the base; spikelets 5.2-6.7 mm long, pedicellate, the pedicels 0.1-0.5 mm long | P. flaccidum |
16. Inner bristles grooved and fused, at least at the base; spikelets 2.5-5.6 mm long, sessile. | → 17 |
17. Inner bristles fused for up to 1/4 their length; many outer bristles exceeding the spikelets; terminal bristles 10.5-23 mm, noticeably longer than the other bristles in the fascicles | P. ciliare |
17. Inner bristles fused for 1/3 – 1/2 their length; outer bristles not exceeding the spikelets; terminal bristles 2.9-6.5 mm, usually not noticeably longer than other bristles in the fascicles | P. setigerum |
15. Lower portion of the rachises pubescent. | → 18 |
18. Plants 200-800 cm tall; midculm leaves (4)12-40 mm wide; panicles golden-yellow or dark purple; rachises with 30-40 fascicles per cm | P. purpureum |
18. Plants 50-200 cm tall; midculm leaves 2-11 mm wide; panicles white, burgundy, light purple, or pink; rachises with 5-17 fascicles per cm. | → 19 |
19. Midculm leaves 2-3.5 mm wide, convolute or folded, green, the midvein noticeably thickened; lower florets of the spikelets usually sterile, sometimes staminate | P. setaceum |
19. Midculm leaves 3-11 mm wide, flat, green or burgundy, the midvein not noticeably thickened; lower florets of the spikelets staminate. | → 20 |
20. Plants shortly rhizomatous; nodes pubescent; panicles erect to slightly arching, white or purple-tinged; leaves green; ligules 1-1.7 mm long; fascicles with 0-24 terete, scabrous outer bristles | P. orientale |
20. Plants not rhizomatous; nodes glabrous; panicles conspicuously drooping, burgundy (rarely whitish-green); leaves burgundy (rarely green); ligules 0.5-0.8 mm long; fascicles with 43-68 terete, scabrous outer bristles | P. advena |
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