Panicum

Plants annual or perennial; their habit variable. Culms 2-300 cm, herbaceous, sometimes hard and almost woody, or woody, simple or branched, bases sometimes cormlike; internodes solid, spongy, or hollow. Leaves cauline, basal, or both, basal leaves not forming a winter rosette; ligules membranous, usually ciliate; blades filiform to ovate, flat to involute, glabrous or pubescent, cross sections with Kranz anatomy and 1 or 2 bundle sheaths or with non-Kranz anatomy; photosynthesis C4 with NAD-me or NADP-me pathways, or, in plants with non-Krantz anatomy, C3. Inflorescences terminal on the culms and branches, often also axillary, terminal panicles typically appearing after midsummer; sterile branches and bristles absent; disarticulation usually below the glumes, sometimes at the base of the upper florets, if at the base of the upper florets, then the florets not very plump at maturity. Spikelets 1-8 mm, usually dorsally compressed, some¬times subterete or laterally compressed, unawned. Glumes usually unequal, herbaceous, glabrous or pubescent, rarely tuberculate or glandular, apices not or only slightly gaping at maturity; lower glumes minute to almost equaling the spikelets, 1-9-veined, truncate, acute, or acuminate; upper glumes slightly shorter to much longer than the spikelets, 3-13(15)-veined, bases rarely slightly sulcate, apices rounded to attenuate; lower florets sterile or staminate; lower lemmas similar to the upper glumes; lower paleas absent, or shorter than the lower lemmas and hyaline; upper florets bisexual, sessile or stipitate, apices acute, puberulent, or with a tuft of hairs; upper lemmas usually more or less rigid and chartaceous-indurate, usually shiny, glabrous or (rarely) pubescent, usually smooth, sometimes verrucose or transversely rugose, margins involute, usually clasping the paleas, rarely with basal wings or lunate scars, apices obtuse, acute, apiculate, or with small green crests; upper paleas striate, rarely transversely rugose; lodicules 2; anthers usually 3. Caryopses smooth; pericarp thin; endosperm hard, without lipid, starch grains simple or compound, or both; hila round or oval, x = 9 (usually), sometimes 10, with polyploid and dysploid derivatives.

Distribution

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

Discussion

Panicum is a large genus, but just how large is difficult to estimate because its limits are not yet clear. Many taxonomists would treat it as including Dichanthelium, Steincbisma, and some members of Urochloa. Recent work supports some aspects of the treatment presented here, but not all of them. For instance, Guissani et al. (2001) suggest that Panicum subg. Panicum is a monophyletic group that should have a rank equivalent to Dichanthelium and Steinchisma. The two other subgenera included here in Panicum, subg. Agrostoidea and subg. Phanopyrum, are not monophyletic, but the relationships of their species to other members of Panicum sensu lato are not well enough understood to suggest a better treatment, nor to justify the name changes a differing generic treatment would require.

Most species of Panicum are tropical, but many grow in warm, temperate regions. Of the thirty-four species occurring in the Flora region, twenty-five are native, seven are established introductions, and two are not established within the region. Within the Flora region, Panicum is most abundant in the southeastern United States. Many species grow in early serai stages or weedy areas; some grow at forest edges, in prairies, savannahs, deserts, forests, beaches, and in shallow water.

Panicum miliaceum has been grown since prehistory in China and India as a cereal grain, and is a common component of bird seed. Seeds of P. hirticaule subsp. sonorum have been used for food by the Cocopa tribe of the southwest. Important hay and range species include P. virgatum, P. rigidulum, P. bulbosum, P. obtusum, and P. repens.

Apomixis, polyploidy, and autogamy have produced numerous microspecies in some groups; hybridization and introgression has resulted in a reticulum of intergrading forms in some complexes. The number of taxa recognized has varied widely over the past century.

Selected References

Darbyshire, S.J. and J. Cayouette. 1995. Identification of the species in the Panicum capillare complex (Poaceae) from eastern Canada and adjacent New York State. Canad. J. Bot. 73:333-348

Guissani, L.M., J.H. Cota-Sanchez, E.O. Zuloaga, and E.A. Kellogg. 2001. A molecular phylogeny of the grass subfamily Panicoideae (Poaceae) shows multiple origins of C4 photosynthesis. Amer. J. Bot. 88:1993-2001

Hitchcock, A.S. and A. Chase. 1910. The North American species of Panicum. Contr. U.S. Natl. Herb. 15:1-396

Hitchcock, A.S. 1951 [title page 1950]. Manual of the Grasses of the United States, ed. 2, rev. A. Chase. U.S.D.A. Miscellaneous Publication No. 200. U.S. Government Printing Office, Washington, D.C., U.S.A. 1051 pp.

Reed, C.F. 1964. A flora of the chrome and manganese ore piles at Canton, in the Port of Baltimore, Maryland and at Newport Newo, Virginia, with descriptions of genera and species new to the flora of the eastern United States. Phytologia 10:321-405

Zuloaga, F.O. 1987. Systematics of New World Species of Panicum (Poaceae: Paniceae). Pp. 287-306 in T.R. Soderstrom, K.W. Hilu, C.S. Campbell, and M.E. Barkworth (eds.). Grass Systematics and Evolution. Smithsonian Institution Press, Washington, D.C., U.S.A. 473 pp.

Zuloaga, F.O. and O. Morrone. 1996. Revision de las especies Americanas de Panicum subgenera Panicum section Panicum (Poaceae: Panicoideae: Paniceae). Ann. Missouri Bot. Gard. 83:200-280.

Lower Taxa

Panicum subg. Agrostoidea, Panicum subg. Panicum, Panicum subg. Phanopyrum

Key

1	Panicle branches 1-sided; spikelets usually subsessile, the longest pedicels usually less than 2 mm long, rarely 3 mm long.	> 2
2	Spikelets 5.5-7 mm long; upper florets less than 1/3 as long as the spikelets (sect. Phanopyrum)	Panicum gymnocarpon
2	Spikelets 1.6-4.4 mm long; upper florets 2/5 as long as to almost equaling the spikelets.	> 3
3	Lower glumes 5- or 7-veined, about 3/4 as long as the spikelets; plants with stolons or shallow rhizomes (sect. Obtusa)	Panicum obtusum
3	Lower glumes 1- or 3-veined, 1/2 - 2/3 as long as the spikelets; plants without stolons, often with rhizomes.	> 4
4	Lower florets staminate; lower paleas subequal to the lower lemmas; upper thin, lemmas flexible, clasping the paleas only at the base (sect. Hemitonia)	Panicum hemitomon
4	Lower florets sterile; lower paleas no more than 2/3 as long as the lower lemmas; upper lemmas thick, stiff, clasping the paleas throughout their length.	> 5
5	Glumes and lower lemmas without keeled midveins; upper florets with glabrous apices; plants tufted, from knotty rhizomes; panicles with a few spikelets; pedicels with slender hairs near the apices (sect. Tenera)	Panicum tenerum
5	Glumes and lower lemmas with keeled midveins; upper florets with a tuft of small hairs at the apices; plants often with scaly rhizomes; panicles with many spikelets; pedicels glabrous (sect. Agrostoidea).	> 6
6	Plants without conspicuous rhizomes, cespitose; culms and sheaths strongly compressed; spikelets usually 1.6-3.8 mm long, lanceolate, not falcate	Panicum rigidulum
6	Plants with conspicuous, stout, short or elongate, scaly rhizomes; culms and sheaths slightly compressed; spikelets 2.3-3.9 mm long, rarely lanceolate, often falcate	Panicum anceps
1	Panicle branches usually not 1-sided; spikelets not subsessile, the longest pedicels 2-20 mm long.	> 7
7	Upper glumes and lower lemmas warty-tuberculate (sect. Verrucosa).	> 8
8	Lower lemmas verrucose with hemispheric warts; spikelets 1.7-2.2 mm long, about 1 mm wide, subacute or obtuse, glabrous; plants of wetlands	Panicum verrucosum
8	Lower lemmas tuberculate-hispid; spikelets 3.2-4 mm long, about 1.5 mm wide, acute or acuminate; plants of dry, sandy or clayey areas	Panicum brachyanthum
7	Upper glumes and lower lemmas glabrous, villous, or scabridulous, but not warty-tuberculate.	> 9
9	Upper florets faintly to evidently transversally rugose; sheaths keeled; culm bases often cormlike (sect. Bulbosa).	> 10
10	Culm bases thickened, cormlike; culms slightly compressed; rhizomes, if present, short and thin; spikelets 2.8-5.4 mm long; lower glumes 1.2-3.5 mm long, 1/2 - 4/5 as long as the spikelets	Panicum bulbosum
10	Culm bases not cormlike; culms strongly compressed; rhizomes present, long, stout; spikelets 2.5-3.4 mm long; lower glumes usually less than 1.7 mm long, up to 1/2 as long as the spikelets	Panicum plenum
9	Upper florets smooth or striate, rarely inconspicuously rugose; sheaths not keeled; culm bases never cormlike.	> 11
11	Plants with rhizomes about 1 cm thick and with large, pubescent, scalelike leaves; culms hard, almost woody (sect. Antidotalia)	Panicum antidotale
11	Plants without rhizomes or with rhizomes less than 0.5 cm thick and with small, glabrous, scalelike leaves; culms clearly not woody, except at the base of P. hirsutum (subg. Panicum).	> 12
12	Glumes, lower lemmas, and upper lemma margins villous, with whitish hairs (sect. Urvilleana)	Panicum urvilleanum
12	Glumes and lemmas usually glabrous, sometimes the lower lemmas sparsely pilose on the margins and near the apices.	> 13
13	Plants perennial, usually with vigorous scaly rhizomes; lower florets staminate (sect. Repentia).	> 14
14	Lower glumes 0.5-1.5 mm long, less than 1/2 as long as the spikelet, 1-5-veined; upper glumes and lower lemmas extending 0.1-0.5 mm beyond the upper florets and scarcely separated (gaping); lower paleas oblong, not hastate-lobed.	> 15
15	Lower glumes subtruncate to broadly acute, faintly veined; upper florets widest at or above the middle, with rounded apices; plants not cespitose, with long, scaly rhizomes	Panicum repens
15	Lower glumes acute, with evident veins; upper florets widest below the middle, with lightly beaked apices; plants cespitose, with short knotty rhizomes	Panicum coloratum
14	Lower glumes 1.8-4 mm long, more than 1/2 as long as the spikelets, with at least 5 veins; upper glumes and lower lemmas extending 0.4-3 mm beyond the upper florets, stiffly separated (gaping); lower paleas hastate-lobed.	> 16
16	Panicles contracted; branches appressed to strongly ascending; plants glabrous throughout	Panicum amarum
16	Panicles open; branches ascending to spreading; plants often pilose, at least at the base of the leaf blades	Panicum virgatum
13	Plants annual, or perennials usually without rhizomes, sometimes rooting at the lower nodes; lower florets sterile.	> 17
17	Lower glumes truncate to subacute, 1/5 – 1/3 as long as the spikelets; sheaths more or less compressed, glabrous or sparsely pubescent; plants slightly succulent or spongy (sect. Dichotomiflora).	> 18
18	Plants usually annual, usually terrestrial, rooting at the lower nodes if in water, but not floating; blades 3-25 mm wide	Panicum dichotomiflorum
18	Plants perennial or of indefinite duration, usually aquatic, sometimes floating, rooting at the lower nodes; blades 2-15 mm wide.	> 19
19	Spikelets 2-2.2 mm long; blades 2-4 mm wide; lower paleas absent; culms succulent	Panicum lacustre
19	Spikelets 3-4 mm long; blades 5-15 mm wide; lower paleas present; culms spongy	Panicum paludosum
17	Lower glumes acute to attenuate, usually 1/3 – 3/4 as long as the spikelets; sheaths rounded, usually hirsute or hispid; plants not succulent (sect. Panicum).	> 20
20	Spikelets 4-6.5 mm long.	> 21
21	Upper glumes and lower lemmas only slightly exceeding the upper florets; upper florets 2-2.5 mm wide; plants annual; lower paleas truncate to bilobed	Panicum miliaceum
21	Upper glumes and lower lemmas exceeding the upper florets by 3-4 mm; upper florets 1-1.1 mm wide; plants perennial; lower paleas acute	Panicum capillarioides
20	Spikelets 1-4.2 mm long.	> 22
22	Plants perennial; panicle branches usually with all or most secondary branches confined to the distal 1/3.	> 23
23	Lower panicle branches whorled; culms 2-10 mm thick, 50-300 cm tall.	> 24
24	Sheaths with fragile, prickly hairs causing skin irritation; panicles not breaking at the base and becoming tumble-weeds; lower paleas 1.3-1.7 mm long	Panicum hirsutum
24	Sheaths glabrous or sparsely to densely pubescent but without fragile, prickly hairs; panicles breaking at the base and becoming tumbleweeds; lower paleas 1.4-2.2 mm long	Panicum bergii
23	Lower panicle branches solitary; culms 0.5-10 mm thick, 15-100 cm tall.	> 25
25	Blades glabrous and glaucous on the adaxial surface; nodes sericeous or pilose, sometimes almost glabrous	Panicum hallii
25	Blades sparsely to densely hirsute and not glaucous on the adaxial surface; nodes sericeous.	> 26
26	Spikelets 2.1-2.9 mm long; culms spreading to weakly ascending; blades spreading, 1-5 mm wide, without a prominent white midrib	Panicum diffusum
26	Spikelets 2.6-3.4 mm long; culms erect to decumbent; blades ascending to erect, 0.5-14 mm wide, with a prominent white midrib	Panicum ghiesbreghtii
22	Plants annual; panicle branches usually with secondary branches and pedicels attached to the distal 2/3	> 27
27	Blades 2-7 cm long, 5-20 mm wide, lanceolate, 4-6 times longer than wide (sect. Monticola, in part)	Panicum trichoides
27	Blades 5-40 cm long, 1-18 mm wide, linear, more than 10 times longer than wide (sect. Panicum, in part).	> 28
28	Panicles more than 2 times longer than wide at maturity; branches ascending to somewhat divergent; spikelets narrowly ovoid, usually about 3 times longer than wide	Panicum flexile
28	Panicles less than 1.5 times longer than wide at maturity; branches diverging; spikelets variously shaped, less than 3 times longer than wide.	> 29
29	Spikelets 2.1-4 mm long, upper glumes and lower lemmas with prominent veins; lower glumes 2/5 – 3/4 as long as the spikelets; lower paleas 0.4-2 mm long, from 1/3 as long as the lower lemmas to equaling them; ligules 0.2-0.4 mm or 1-3.5 mm long.	> 30
30	Lower glumes 0.7-1.1 mm long, about 2/5 as long as the spikelets; lower paleas 1-2 mm long; leaf blades 2-8 mm wide, usually completely glabrous, sometimes with a few marginal cilia near the base	Panicum psilopodium
30	Lower glumes 1.2-2.4 mm long, 1/2 - 3/4 as long as the spikelets; lower paleas 0.2-0.9 mm long; leaf blades 1-30 mm wide, hairs papillose-based.	> 31
31	Primary panicle branches appressed to the main axis; culms 2-8 cm long; spikelets 2-2.2 mm long	Panicum mohavense
31	Primary panicle branches divergent; culms 11-110 cm long; spikelets 1.9-4 mm long	Panicum hirticaule
29	Spikelets 1.4-4 mm long, upper glumes and lower lemmas without prominent veins; lower glumes usually less than 1/2 as long as the spikelets; lower paleas usually small or absent; ligules 0.5-1.5 mm long.	> 32
32	Plants mostly glabrous, but the sheaths ciliate on the margins and the blades sometimes sparingly pilose adaxially (sect. Monticola, in part)	Panicum bisulcatum
32	Plants mostly hairy, even the sheaths hairy throughout.	> 33
33	Panicles usually more than 1/2 the total height of the plant, breaking at the base of the peduncle at maturity and becoming a tumbleweed; spikelets 1.9-4 mm long; mature upper florets stramineous or nigrescent (sect. Panicum, in part)	Panicum capillare
33	Panicles usually less than 1/2 the total height of the plant, the base of the peduncle usually not breaking at maturity; spikelets 1.4-2.4 mm long; mature upper florets often dark brown	Panicum philadelphicum