Sporobolus

Plants annual or perennial; usually cespitose, sometimes rhizomatous, rarely stoloniferous. Culms 10-250 cm, usually erect, rarely prostrate, glabrous. Sheaths open, usually glabrous, often ciliate at the apices; ligules of hairs; blades flat, folded, involute, sometimes terete. Inflorescences terminal, open or contracted panicles, sometimes partially included in the upper¬most sheath. Spikelets rounded to laterally compressed, with 1(-3) floret(s) per spikelet; disarticulation above the glumes. Glumes 0-1-veined; calluses poorly developed, usually glabrous; lemmas membranous or chartaceous, 1(3)-veined, unawned; paleas glabrous, 2-veined, often splitting between the veins at maturity; anthers (2)3. Fruits utricles or achenes, ellipsoid, obovoid, fusiform, or quadrangular, pericarp free from the seed, becoming mucilaginous when moist in most species, remaining dry and partially adherent to the seed in 5. heterolepis and 5. clandestinus. Cleistogamous spikelets occasionally present in the lower leaf sheaths, x = 9.

Distribution

Conn., N.J., N.Y., Wash., Va., W.Va., Del., D.C, Wis., Ariz., N.Mex., Pacific Islands (Hawaii), Mich., N.Dak., Alta., B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask., Mass., Maine, N.H., R.I., Vt., Fla., Miss., Utah, Wyo., Oreg., Tex., La., S.C., N.C., Nebr., Tenn., Pa., Ala., Iowa, Ill., Ind., Ky., Md., Ohio, Nev., Puerto Rico, Kans., Mo., Okla., Colo., Ga., Virgin Islands, Calif., Ark., Idaho, Minn., S.Dak., Mont.

Discussion

Sporobolus is a cosmopolitan genus of more than 160 species that grow in tropical, sub¬tropical, and warm-temperate regions throughout the world. Seventy-three species are native to the Western Hemisphere; 27 are native to the Flora region, three are established introductions, and one was introduced but has not persisted. Two genera of the Western Hemisphere, Calamovilfa and Crypsis, resemble Sporobolus in having hairy ligules, spikelets with 1 floret, 1-veined lemmas, and fruits with a free pericarp (Peterson et al. 1997).

Selected References

Baaijens, G.J. and J.F. Veldkamp. 1991. Sporobolus (Gramineae) in Malesia. Blumea 35:393-458

Lasgaard, S. and RM. Peterson. 2001. Flora of Ecuador 68 (ed. G. Harling & L. Andersson). 214(2). Gramineae (part 2): Subfam. Chloridoideae. Botanical Institute, University of Goteborg, Goteborg, Sweden and Section for Botany, Riksmuseum, Stockholm, Sweden. 131 pp.

McGregor, R.L. 1990. Seed dormancy and germination in the annual cleistogamous species of Sporobolus (Poaceae). Trans. Kansas Acad. Sci. 93:8-11

Peterson, P.M., R.D. Webster and J. Valdes-Reyna. 1997. Genera of New World Eragrostideae (Poaceae: Chloridoideae). Smithsonian Contr. Bot. 87:1-50

Riggins, R. 1977. A biosystematic study of the Sporobolus asper complex (Gramineae). Iowa State J. Res. 51:287-321

Simon, B.K. and S.W.L. Jacobs. 1999. Revision of the genus Sporobolus (Poaceae, Chloridoideae) in Australia. Austral. J. Bot. 12:375-148

Weakley, A.S. and P.M. Peterson. 1998. Taxonomy of the Sporobolus floridanus complex (Poaceae: Sporobolinae). Sida 18:247-270.

Lower Taxa

Sporobolus airoides, Sporobolus buckleyi, Sporobolus clandestinus, Sporobolus coahuilensis, Sporobolus compositus, Sporobolus contractus, Sporobolus creber, Sporobolus cryptandrus, Sporobolus curtissii, Sporobolus diandrus, Sporobolus domingensis, Sporobolus fimbriatus, Sporobolus flexuosus, Sporobolus floridanus, Sporobolus giganteus, Sporobolus heterolepis, Sporobolus indicus, Sporobolus interruptus, Sporobolus jacquemontii, Sporobolus junceus, Sporobolus nealleyi, Sporobolus neglectus, Sporobolus pinetorum, Sporobolus purpurascens, Sporobolus pyramidatus, Sporobolus silveanus, Sporobolus tenuissimus, Sporobolus teretifolius, Sporobolus texanus, Sporobolus vaginiflorus, Sporobolus virginicus, Sporobolus wrightii

Key

1	Plants annuals or short-lived perennials flowering in the first year.	> 2
2	Lower panicle nodes with 7-20 branches	> 3
3	Pedicels 0.1-0.5(1) mm long, appressed	Sporobolus pyramidatus
3	Pedicels 2(3)-6(8) mm long, widely spreading	undefined
2	Lower panicle nodes with 1-3 branches	> 4
4	Spikelets 0.7-1.1 mm long; anthers 0.2-0.3 mm long	Sporobolus tenuissimus
4	Spikelets 1.6-6 mm long; anthers 0.3-3.2 mm long.	> 5
5	Mature panicles 10-35 cm long, 4.5-30 cm wide, open; secondary branches spreading; pedicels usually 6-25 mm long, spreading	Sporobolus texanus
5	Mature panicles 1-5 cm long, 0.2-0.5 cm wide, contracted; secondary branches appressed; pedicels usually 0.1-4 mm long, appressed.	> 6
6	Lemmas strigose; spikelets 2.3-6 mm long; mature fruits (1.1)1.8-2.7 mm long	Sporobolus vaginiflorus
6	Lemmas glabrous; spikelets 1.6-3 mm long; mature fruits 1.2-1.8 mm long	Sporobolus neglectus
1	Plants perennial.	> 7
7	Plants with rhizomes.	> 8
8	Spikelets 1.4-3.2 mm long.	> 9
9	Panicles 0.4-1.6 cm wide, spikelike, blades usually conspicuously distichous	Sporobolus virginicus
9	Panicles 2.4-8 cm wide, somewhat contracted to lax and open, blades not obviously distichous	Sporobolus fimbriatus
8	Spikelets 4-10 mm long.	> 10
10	Panicles (0.6)1-8 cm wide, open to somewhat contracted, narrowly pyramidal, well-exerted from the uppermost sheath; branches without spikelets on the lower 1/3	Sporobolus interruptus
10	Panicles 0.04-1.6 cm wide, narrow or spikelike, partially to wholly included in the uppermost sheath; branches spikelet-bearing to the base.	> 11
11	Fruits 1-2 mm long; pericarp gelatinous, slipping from the seed when wet; panicles 5-30 cm long, 0.4-1.6 cm wide; lemmas glabrous, smooth	Sporobolus compositus
11	Fruits (1.5)2.4-3.5 mm long; pericarp loose but neither gelatinous nor slipping from the seed when wet; panicles 5-11 cm long, 0.04-0.3 cm wide; lemmas minutely pubescent or scabridulous	Sporobolus clandestinus
7	Plants without rhizomes.	> 12
12	Upper glumes usually less than 2/3 as long as the florets.	> 13
13	Lower panicle branches much shorter than the adjacent internodes, appressed to strongly ascending	Sporobolus creber
13	Lower panicle branches usually as long as or longer than the adjacent internodes, appressed or ascending.	> 14
14	Spikelets 2-2.7 mm long; upper glumes usually 1/2 - 2/3 as long as the florets, acute to obtuse, entire	Sporobolus indicus
14	Spikelets 1.3-1.8(2) mm long; upper glumes usually less than 1/2 as long as the florets, rarely longer; truncate, erose to denticulate.	> 15
15	Anthers 0.9-1.1 mm long, usually 3, rarely 2; branches spikelet-bearing to the base	Sporobolus jacquemontii
15	Anthers 0.5-0.8 mm long, usually 2, rarely 3; branches without spikelets on the lower 1/4	Sporobolus diandrus
12	Upper glumes at least 2/3 as long as the florets, often longer.	> 16
16	Spikelets 1-2.5(2.8) mm long [for opposite lead, see p. 117].	> 17
17	Lower sheaths keeled and flattened below	Sporobolus buckleyi
17	Lower sheaths rounded below.	> 18
18	Panicles 12-35 cm wide, open.	> 19
19	Sheath apices with a conspicuous tuft of white hairs; flag blades nearly perpendicular to the culms	Sporobolus cryptandrus
19	Sheath apices glabrous or with a few scattered hairs; flag blades ascending.	> 20
20	Secondary panicle branches spikelet-bearing to the base; pedicels mostly appressed, mostly 0.2-0.5 mm long; panicles 20-60 cm long	Sporobolus wrightii
20	Secondary panicle branches without spikelets on the lower 1/4 - 1/2; pedicels mostly spreading, mostly 0.5-25 mm long; panicles 10-45 cm long.	> 21
21	Pedicels 0.5-2 mm long; anthers 1.1-1.8 mm long	Sporobolus airoides
21	Pedicels 6-25 mm long; anthers 0.3-1 mm long	Sporobolus texanus
18	Panicles 0.2-12(14) cm wide, contracted to open.	> 22
22	Mature panicles 0.2-5 cm wide, contracted, often spikelike, the panicle branches appressed or diverging no more than 30° from the rachises.	> 23
23	Primary panicle branches without spikelets on the lower 1/8–1/2 of their length.	> 24
24	Leaf blades 1-1.5 mm wide; ligules 0.2-0.4 mm long	Sporobolus nealleyi
24	Leaf blades 2-6 mm wide; ligules 0.3-1 mm long.	> 25
25	Lower panicle nodes with 7-12(15) branches; anthers 0.2-0.4 mm long	Sporobolus pyramidatus
25	Lower panicle nodes with 1-3 branches; anthers 0.5-1 mm long	Sporobolus cryptandrus
23	Primary panicle branches spikelet-bearing to the base.	> 26
26	Lower glumes usually 1-veined; mature panicles 0.2-0.8(1) cm wide; lemmas 2-3.2 mm long, linear-lanceolate; upper glumes 2-3.2 mm long; anthers 3, 0.3-0.5 mm long; plants primarily from west of the Mississippi River	Sporobolus contractus
26	Lower glumes usually without veins; mature panicles 1-5 cm wide; lemmas 1.1-2 mm long, ovate; upper glumes 1.1-2 mm long; anthers 2 or 3, 0.5-1 mm long; plants primarily from east of the Mississippi River	Sporobolus domingensis
22	Mature panicles 4.5-30 cm wide, open, pyramidal to subovate or oblong, the panicle branches diverging more than 10° from the rachises, sometimes reflexed.	> 27
27	Lower panicle nodes with 7-12(15) branches; anthers 0.2-0.4 mm long	Sporobolus pyramidatus
27	Lower panicle nodes with 1-2(3) branches; anthers 0.4-1 mm long.	> 28
28	Pedicels 6-25 mm long, spreading; panicles 4.5-30 cm wide, about as long as wide, diffuse	Sporobolus texanus
28	Pedicels 0.1-3 mm long, appressed or spreading; panicles 0.3-14 cm wide, longer than wide, open and/or drooping.	> 29
29	Culms 10-50(60) cm tall, 0.7-1.2 mm thick near the base; plants with hard, knotty bases; blades (0.6)1.5-6(7) cm long, 1-1.5 mm wide, involute, spreading at right angles to the culms	Sporobolus nealleyi
29	Culms 30-120 cm tall, 1-3.5 mm thick near the base; plant bases not hard and knotty; blades (2)5-26 cm long, 2-6 mm wide, flat to involute, ascending or at right angles to the culms.	> 30
30	Pedicels appressed to the secondary branches; primary branches appressed, spreading, or reflexed; pulvini glabrous; rachises straight, erect; mature panicles narrowly pyramidal, lower branches longer than the middle branches	Sporobolus cryptandrus
30	Pedicels spreading from the secondary branches; primary branches reflexed; pulvini pubescent; rachises drooping or nodding; mature panicles subovate to oblong, lower branches no longer than those in the middle	Sporobolus flexuosus
16	Spikelets 2.5-10 mm long [for opposite lead, see p. 116].	> 31
31	Lower panicle nodes with 3 or more branches.	> 32
32	Mature panicles 2-6 cm wide, pyramidal; panicle branches diverging 20-100° from the rachises; blades 0.8-2 mm wide; fruits 1.4-1.8 mm long	Sporobolus junceus
32	Mature panicles 0.4-1.6 cm wide, narrow, contracted; panicle branches appressed or diverging to 20° from the rachises; blades 2-5 mm wide; fruits 1.8-2.3 mm long	Sporobolus purpurascens
31	Lower panicle nodes with 1-2(3) branches.	> 33
33	Mature panicles 0.04-4 cm wide, spikelike; panicle branches appressed.	> 34
34	Spikelets 4-6(10) mm long, stramineous to purplish-tinged; panicles terminal and axillary; sheaths without a conspicuous apical tuft of hairs.	> 35
35	Lemmas minutely pubescent or scabridulous, chartaceous and opaque; pericarps loose but neither gelatinous nor slipping off the seeds when wet; fruits (1.5)2.4-3.5 mm long	Sporobolus clandestinus
35	Lemmas usually glabrous and smooth, membranous to chartaceous and hyaline; pericarps gelatinous, slipping off the seeds when wet; fruits 1-2 mm long	Sporobolus compositus
34	Spikelets 1.7-3.5(4) mm long, whitish to plumbeous; panicles all terminal; sheaths with a conspicuous apical tuft of hairs.	> 36
36	Culms 40-100(120) cm tall, 2-4(5) mm thick near the base; mature panicles 0.2-0.8(1) cm wide; anthers 0.3-0.5 mm long	Sporobolus contractus
36	Culms 100-200 cm tall, (3)4-10 mm thick near the base; mature panicles 1-4 cm wide; anthers 0.6-1 mm long	Sporobolus giganteus
33	Mature panicles (0.6)1-30 cm wide, usually open, narrowly pyramidal to pyramidal or ovate; panicle branches appressed or spreading.	> 37
37	Spikelets 2.3-3 mm long; panicles 4.5-30 cm wide, diffuse, about as long as wide; branches capillary; anthers 0.3-1 mm long	Sporobolus texanus
37	Spikelets 3-7.2 mm long; panicles 0.6-15 cm wide, longer than wide, not diffuse; branches not capillary; anthers 1.5-5 mm long.	> 38
38	Mature spikelets plumbeous; sheath bases dull, fibrous.	> 39
39	Anthers 3-4.2 mm long; ligules 0.2-0.7 mm long; plants from Arizona	Sporobolus interruptus
39	Anthers 1.7-3 mm long; ligules 0.1-0.3 mm long; plants not known from Arizona	Sporobolus heterolepis
38	Mature spikelets purplish-brown to purplish; sheath bases shiny, indurate.	> 40
40	Blades 0.5-1.2 mm wide, subterete to terete in cross section, at least at the base, sometimes channeled for portions of their length, sometimes becoming tightly involute distally, senescing or turning tan in late fall, the margins smooth; pedicels with scattered ascending hairs	Sporobolus teretifolus
40	Blades 0.8-10 mm wide, flat or V-shaped in cross section, flat, folded, or involute when dry, remaining green well into winter or yellowing at maturity, the margins usually scabridulous, occasionally smooth; pedicels glabrous, sometimes scabridulous or scabrous.	> 41
41	Lower glumes from 0.9 times as long as to longer than the upper glumes; culms 30-80(90) cm tall; panicles 10-25 cm long; pedicels 0.5-4(8) mm long, usually shorter than the spikelets, appressed	Sporobolus curtissii
41	Lower glumes from 0.6-0.9 (0.94) times as long as the upper glumes; culms (30)45-250 cm tall; panicles 15-50 cm long; pedicels 2-22 mm long, spreading or appressed.	> 42
42	Pedicels appressed; lemmas 4.4-6.5 mm long; anthers 3.5-5 mm long; spikelets purplish	Sporobolus silveanus
42	Pedicels spreading; lemmas 3-4.3 mm long; anthers 2-3.4 mm long; spikelets purplish-brown.	> 43
43	Blades (2)3-10 mm wide, pale bluish-green, yellowing at maturity; panicles (18)30-50 cm long, 4-15 cm wide; lower glumes (0.6)0.75-0.94 times as long as the upper glumes	Sporobolus floridanus
43	Blades 1.2-2(3) mm wide, dark green, remaining green well into winter; panicles 15-30 cm long, 2-6 cm wide; lower glumes 0.6-0.83 times as long as the upper glumes	Sporobolus pinetorum