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
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. | > 2 |
| 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. | > 8 |
| 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. | > 10 |
| 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. | > 15 |
| 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. | > 14 |
| 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). | > 18 |
| 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. | > 21 |
| 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. | > 24 |
| 25 | Blades glabrous and glaucous on the adaxial surface; nodes sericeous or pilose, sometimes almost glabrous | Panicum ballii |
| 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 | > 23 |
| 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 mobavense |
| 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. | > 30 |
| 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 |
"decumbent" is not a number.