25.10   PANICUM L.

REVISED TREATMENT. Treatment revised by Mary Barkworth on April 25, 2007 to exclude Hopia, Phanopyrum, and Zuloagaea.
Please send comments to Mary Barkworth.

Plants annual or perennial; their habit variable. Culms 2-300 cm, herbaceous, sometimes hard and almost woody, or woody, simple or branched, bases not 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 C₄with 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, sometimes 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, 2/3 as long as to equaling or exceeding the upper glume, 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, and smooth, sometimes pubescent, sometimes verrucose or faintly 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. Name from the Latin panis, bread, or panus, an ear of millet.

Panicum is a large genus, but just how large is difficult to estimate because its limits are not yet clear. The treatment presented here differs from that in FNA 25 in the transfer of P. obtusum to Hopia obtusa (Zuloaga et al. 2007), of P. gymnocarpum to Phanopyrum gymnocarpum (Aliscioni et al. 2003; Zuloaga et al. 2007), and of P. bulbosum and P. plenum to Zuloagaea bulbosa (Bess et al. 2006). The articles cited provide the justification for the changes.

Most species of Panicum are tropical, but many grow in warm, temperate regions. Of the thirty species occurring in the Flora region, twenty-one 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 seral 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, 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.

Panicum L. subg. Panicum

Plants annual or perennial; usually cespitose. Culms usually erect, not compressed. Sheaths not keeled; ligules of hairs, or membranous and, usually, ciliate; blades with vascular bundles separated by 2–6 radially arranged, tabular mesophyll cells and surrounded by a double sheath, cells of the inner sheath thick-walled, cells of the outer sheath with thinner cell walls and usually centripetal chloroplasts; chloroplasts with well-developed grana. Photosynthesis C₄ NAD-me type. Panicles usually pyramidal, lax and diffuse, varying to contracted and condensed; secondary branches usually present; pedicels divergent to more or less appressed. Spikelets ellipsoid to lanceolate, glabrous. Lower glumes 1/5–4/5 the length of the spikelets, 1–11-veined; upper glumes and lower lemmas (5)7–15-veined; lower florets usually sterile; upper florets smooth, shining; upper paleas with compound or compound and simple papillae towards the apices. x = 9.

There are approximately 50 species of Panicum subg. Panicum in the Western Hemisphere (Zuloaga 1987), 21 of which grow in the Flora region.

Panicum L. sect. Panicum

Plants annual or perennial; perennials usually cespitose, sometimes shortly rhizomatous. Culms 2–300 cm, erect or decumbent, not succulent, sometimes almost woody at the base, often branching from the lower nodes. Sheaths not compressed. Panicles usually lax and diffuse; pedicels divergent. Spikelets ellipsoid to lanceoloid, glabrous. Lower glumes ( 1/3)1/2–3/4 as long as the spikelets, (3)5–7-veined, truncate, obtuse, acute, or acuminate; lower paleas present or absent.

Panicum sect. Panicum includes approximately 22 species and extends from the southern United States to Argentina. Most species grow in dry, open places, but a few grow in moist sites such as river banks.

1.   Panicum miliaceum L.
Broomcorn, Hog Millet, Panic Millet, Millet Commun

Plants annual; sometimes branching from the lower nodes. Culms 20-210 cm, stout, not woody; nodes puberulent; internodes usually with papillose-based hairs, sometimes nearly glabrous, not succulent. Leaves numerous; sheaths terete, densely pilose, with papillose-based and caducous hairs; ligules membranous, ciliate, cilia 1-3 mm; blades 15-40 cm long, 7-25 mm wide. Panicles 6-20 cm long, 4-11 cm wide, included or shortly exserted at maturity, dense; branches stiff, appressedto spreading, spikelets solitary, confined to the distal portions; pedicels 1-9 mm, scabrous and sparsely pilose. Spikelets 4-6 mm, ovoid, usually glabrous. Lower glumes 2.8-3.6 mm, 1/2-3/4 as long as the spikelets, 5-7-veined, veins scabridulous distally, apices attenuate; upper glumes 4-5.1 mm, slightly exceeding the upper florets, 11-13(15)-veined, veins scabridulous distally; lower florets sterile; lower lemmas 4-4.8 mm, slightly exceeding the upper florets, 9-13-veined, veins scabridulous distally; lower paleas 1.2-1.6 mm, 1/2 or less the length of the upper florets, truncate to bilobed; upper florets 3-3.8 mm long, 2-2.5 mm wide, smooth or striate, more or less shiny, stramineous to orange, red-brown, or blackish, persisting in the spikelets or disarticulating at maturity. 2n = 36, 40, 42, 49, 54, 72.

Panicum miliaceum is native to Asia, where it has been cultivated for thousands of years. In the Flora region, it is grown for bird seed and is occasionally planted for game birds. It is also found in corn fields and along roadsides. In Asia, P. miliaceum is still grown for fodder and as a cereal, its fast germination and short growth period enabling it to be sown following a spring crop. It also has one of the lowest water requirements of any cereal grain.

Panicum miliaceum L. subsp. miliaceum

Culms 20-120 cm. Panicles more than twice as long as wide, relatively contracted, usually nodding, not fully exserted; branches ascending to appressed; pulvini almost absent. Upper florets stramineous to orange, not disarticulating at maturity.

Panicum miliaceum subsp. miliaceum is the subspecies used in bird seed. It probably rarely persists because of the retention of the upper florets on the plant and, in northern states, poor seed survival over winter.

Panicum miliaceum subsp. ruderale (Kitag.) Tzvelev

Culms 70-210 cm. Panicles about twice as long as wide, open, erect, exserted; branches ascending to spreading; pulvini well-developed. Upper florets blackish, shiny, disarticulating at maturity.

Panicum miliaceum subsp. ruderale is now naturalized over much of the Flora region. It may become a major weed, especially in corn fields.

2.   Panicum capillare L.
Witchgrass, Panic Capillaire

Plants annual; hirsute or hispid, hairs papillose-based, often bluish or purplish. Culms 15-130 cm, slender to stout, not woody, erect to decumbent, straight to zigzag, simple to profusely branched; nodes sparsely to densely pilose. Sheaths rounded, hirsute or hispid, hairs papillose-based; ligules membranous, ciliate, cilia 0.5-1.5 mm; blades 5-40 cm long, 3-18 mm wide, linear, spreading. Panicles 13-50 cm long, 7-24 cm wide, usually more than 1/2 as long as the plants, included at the base or exserted at maturity, disarticulating at the base of the peduncles at maturity and becoming a tumbleweed; branches spreading; pedicels 0.5-2.8 mm, scabrous, pilose. Spikelets 1.9-4 mm, ellipsoid to lanceoloid, often red-purple, glabrous. Lower florets sterile; lower glumes 1/3-1/2 as long as the spikelets, 1-3-veined; upper glumes 1.8-3.1 mm, 7-9-veined, midveins scabridulous; lower lemmas 1.9-3 mm, extending 0.4-1.1 mm beyond the upper florets, often stiff, straight, prominently veined distally; upper florets stramineous or nigrescent, sometimes with a prominent lunate scar at the base, often disarticulating before the glumes, leaving the empty glumes and lower lemmas temporarily persisting on the panicles. 2n = 18.

Panicum capillare grows in open areas, particularly in disturbed sites such as fields, pastures, roadsides, waste places, ditches, sand, rock crevices, etc. It grows throughout temperate North America, including northern Mexico. It also grows in Bermuda, the Virgin Islands, and sporadically in South America, and has become naturalized in much of Europe and Asia. It appears to hybridize with P. philadelphicum.

Panicum capillare L. subsp. capillare

Culms medium to robust, ascending to erect, rarely delicate or spreading, usually green or red-purple, rarely bluish-green, often branching at the base. Panicle branches spreading; secondary branches and pedicels strongly divergent. Spikelets 1.9-4 mm. Lower paleas absent; mature upper florets about 1/2 as wide as long, stramineous or tan, sometimes blackish, without a lunate scar at the base.

Panicum capillare subsp. capillare is the common subspecies, growing in weedy and dry habitats throughout the range of the species. Plants in the western United States and Canada have spikelets over 2.6 mm long more often than those in the east. Robust plants germinating early in the season and growing on better soils tend to spread more, and have wider, shorter blades and more exserted panicles than plants in the eastern United States and Canada growing under comparable conditions. They are sometimes included in P. capillare var. occidentale Rydb., but these traits are not well correlated, and several environmental factors apparently affect their expression. Plants in the eastern part of the range with a well-exserted main panicle at anthesis usually arise from seeds germinating relatively late in the season.

Panicum capillare subsp. hillmanii (Chase) Freckmann & Lelong

Culms often stout and stiff, usually bluish-green, usually not branching at the base. Blades thick, firm. Panicle branches stiff; secondary branches and pedicels usually appressed, varying to narrowly divergent. Spikelets 2.2-3 mm. Lower paleas 1-1.8 mm; mature upper florets nigrescent, with a prominent lunate scar at the base.

Panicum capillare subsp. hillmanii grows in weedy habitats in California, New Mexico, Iowa, Kansas, Oklahoma, and Texas. It may be a southern Great Plains extension of the western plants of subsp. capillare that are sometimes called P. capillare var. occidentale Rydb., but it differs from subsp. capillare in more characters than such plants.

3.   Panicum philadelphicum Bernh. ex Trin.
Philadelphia Witchgrass

Plants annual; hirsute, hairs papillose-based, usually yellow-green to green, sometimes purplish. Culms 8-100 cm tall, about 1 mm thick, erect to decumbent, simple to profusely branched; nodes sparsely to densely pilose. Leaves often crowded basally; sheaths rounded, usually longer than the internodes, hispid, hairs papillose-based, to 5 mm; ligules 0.5-1.5 mm; blades 3-30 cm long, 2-12 mm wide, linear, ascending to erect, flat, hirsute to sparsely pilose, greenish or purplish, bases truncate to subcordate and ciliate on the margins, apices acute. Panicles 7-27 cm long, 4-24 cm wide, 1/4-1/3 as long as the plants, diffuse, usually exserted at anthesis, not breaking at the base of the peduncles to become a tumbleweed; rachises glabrous or sparsely pilose basally; primary branches spreading, secondary branches and pedicels confined to the distal 2/3; secondary branches diverging to appressed, with 1-4 spikelets; pedicels 3-15 mm, spreading to appressed, scabrous or hirsute; pulvini glabrous or pilose. Spikelets 1.4-2.4 mm long, 0.5-0.7 mm wide, usually green, glabrous. Lower glumes 0.5-0.9 mm, usually less than 1/2 as long as the spikelets, 3-4-veined, truncate to acuminate; upper glumes 1.6-2 mm, 7-veined, veins not prominent; lower lemmas 1.6-1.9 mm, 7-9-veined, veins not prominent; lower paleas absent; lower florets sterile; upper florets 1.5-1.7 mm long, about 0.4 mm wide, often dark brown, sometimes disarticulating, apices minutely papillose. 2n = 18.

Panicum philadelphicum grows in open areas such as fallow fields, roadside ditches, receding shores, and rock crevices. It is restricted to the eastern part of the Flora region. It intergrades with P. capillare, possibly as a result of hybridization, especially in the southeastern United States. Seeds germinating on receding shores in late summer often produce tiny plants.

Panicum philadelphicum subsp. gattingeri (Nash) Freckmann & Lelong
Panic de Gattinger

Plants slender to robust. Culms to 100 cm, often spreading to decumbent and rooting at the lower nodes, branching freely distally. Blades 5-12 mm wide, spreading, those of the flag leaves usually more than 1/2 as long as the panicles. Panicles about 1/3 as long as the plant, exserted; secondary branches divergent; pedicels divergent, flexible, scabrous. Spikelets 1.9-2.4 mm. Upper glumes and lower lemmas acuminate, straight; upper florets about 1/2 as wide as long, stramineous, not disarticulating.

Panicum philadelphicum subsp. gattingeri is commonly found in fields, roadsides, and wet clay on receding shores. This subspecies seems to be more common in the warmer parts of the northeastern United States.

2010: Haines demoted subsp. gattingeri to varietal rank, as Panicum philadelphicum var. campestre (Gatt.) A. Haines.

Panicum philadelphicum subsp. lithophilum (Swallen) Freckmann & Lelong

Plants slender, sparsely pilose, purplish. Panicles with a few spikelets; pedicels short, appressed. Spikelets 2-2.1 mm, narrow, less than 1 mm wide. Upper glumes and lower lemmas acuminate; upper florets less than 1/2 as wide as long, blackish at maturity.

Panicum philadelphicum subsp. lithophilum is endemic to wet depressions in granitic outcroppings of Georgia and North and South Carolina.

Panicum philadelphicum Bernh. ex Trin. subsp. philadelphicum
Panic de Philadelphie

Plants often slender, pilose, yellowish-green. Culms erect or decumbent. Blades 2-6 mm wide, often erect, those of the flag leaves usually less than 1/2 as long as the panicles. Secondary panicle branches usually appressed; pedicels usually short, appressed. Spikelets 1.4-2.1 mm, ovoid-ellipsoid, pale green to slightly reddish. Upper glumes and lower lemmas hooked over the upper florets; mature upper florets more than 1/2 as wide as long, shiny, blackish, with several pale veins.

Panicum philadelphicum subsp. philadelphicum grows in meadows, open woods, sand, and on receding shores. Plants with decumbent culms, glabrous pulvini, flexuous pedicels without hairs over 0.2 mm long, spikelets 1.4-1.7 mm long, and the mature floret not disarticulating have been called Panicum tuckermanii Fernald. They are often fairly distinct on receding lake shores in New England and the Great Lakes area (Darbyshire and Cayoutte 1995), but intergrade with subsp. philadelphicum elsewhere.

4.   Panicum flexile (Gatt.) Scribn.
Wiry Witchgrass, Panic Flexible

Plants annual; delicate, green or yellow-green. Culms 10-75 cm, about 1 mm thick, simple or with erect basal branches; nodes densely pilose, hairs ascending; internodes glabrous or shortly pubescent distally. Sheaths longer than the internodes, green to purplish, hispid, margins sparsely ciliate; ligules 0.5-1.5 mm; blades 3-32 cm long, 1-7 mm wide, ascending to erect, linear, narrowing basally, flat or the margins involute, surfaces sparsely hirsute or pilose (rarely glabrous), hairs near the base papillose-based, margins prominent, apices acute. Panicles 5-45 cm long, 1-6 cm wide, at least 1/2 as long as the plants and 3 times longer than wide, open; rachises glabrous; primary branches usually alternate or subopposite, ascending to slightly divergent, secondary branches and pedicels attached to the distal 2/3; secondary branches diverging; pedicels 0.5-17 mm, ascending to appressed. Spikelets 2.5-3.7 mm long, 0.6-1.1 mm wide, narrowly ovoid, glabrous, acute; lower glumes 0.8-1.3 mm, 1/3-1/2 as long as the spikelets, acuminate; upper glumes 2.3-3.3 mm, 7-9-veined, exceeding the upper florets by about 0.6 mm; lower florets sterile; lower lemmas 2.2-2.7 mm, exceeding the upper florets by about 0.6 mm, 7- or 9-veined, apices scabridulous, pointed; lower paleas absent; upper florets 1.6-1.7 mm long, about 0.6 mm wide, usually smooth, usually pale, sometimes becoming dark at maturity. 2n = 18.

Panicum flexile grows in fens and other calcareous wetlands, in dry, calcareous or mafic rock barrens, and in open woodlands, especially on limestone derived soils. It is restricted to the Flora region.

5.   Panicum hirticaule J. Presl
Roughstalked Witchgrass

Plants annual; glabrous or hispid, hairs papillose-based. Culms 11-110 cm, erect to decumbent; nodes shortly hirsute or glabrous. Sheaths shorter than the internodes, greenish to purplish, glabrous or with papillose-based hairs, ciliate on 1 margin, glabrous on the other; collars hirsute;ligules 1.5-3.5 mm, of hairs; blades 3-30 cm long, 3-30 mm wide, flat, usually hirsute or sparsely pubescent, hairs papillose-based, sometimes glabrous, bases rounded to cordate-clasping, margins ciliate, cilia papillose-based, apices acute. Panicles 9-30 cm long, 5-8 cm wide, erect or nodding, partially included to well-exserted, rachises glabrous or sparsely hispid basally; primary branches usually alternate to opposite, divergent, secondary branches and pedicels confined to the distal 2/3; pulvini inconspicuous; secondary branches appressed; pedicels 9-27 mm, appressed. Spikelets 1.9-4 mm long, 0.8-1 mm wide, ovoid to almost spherical, often reddish-brown, glabrous, veins prominent, scabridulous, apices abruptly acuminate. Lower glumes 1.3-2.4 mm, 1/2-3/4 as long as the spikelets, 3-5-veined; upper glumes 1.8-3.3 mm, 7-11-veined; lower florets sterile; lower lemmas similar to the upper glumes, 9-veined; lower paleas 0.4-0.9 mm; upper florets 1.5-2.4 mm long, 0.4-0.8 mm wide, ellipsoid, smooth or conspicuously papillate, shiny, stramineous, often with a lunate scar at the base.

Panicum hirticaule grows in rocky or sandy soils in waste places, roadsides, ravines, and wet meadows along streams. Its range extends from southeastern California and southwestern Texas southward through Mexico, Central America, Cuba, and Hispaniola to western South America and Argentina.

Panicum hirticaule J. Presl subsp. hirticaule

Culms 11-70 cm tall, usually simple; nodes usually hirsute. Sheaths hirsute, hairs papillose-based; Blades 3-16 mm wide, rounded basally. Panicles erect. Spikelets 1.9-3.3 mm. Lower paleas less than 1/2 as long as the upper florets. 2n = 18, 36 (for Panicum pampinosum).

Panicum hirticaule subsp. hirticaule is the most common of the subspecies, growing throughout the range of the species but occurring more often in arid habitats. Panicum alatum Zuloaga & Morrone has recently been described as a new species, differing from P. hirticaule subsp. hirticaule by the presence of paired elaiosomes at the base of a slightly stipitate upper floret. It is known from central Arizona, but apparently is more common in western Mexico.

Panicum hirticaule subsp. sonorum (Beal) Freckmann & Lelong

Culms 60-100 cm, robust; nodes hirsute, hairs papillose-based. Sheaths hirsute, hairs papillose-based; blades 4-30 mm wide, hirsute, hairs papillose-based, cordate, clasping basally. Panicles nodding. Spikelets 3-3.3 mm; lower paleas more than 1/2 as long as the upper florets. 2n = unknown.

Panicum hirticaule subsp. sonorum has been collected only a few times. Its range extends from southern Arizona to Chiapas, Mexico. It may have originated through selection and cultivation. The Cocopa tribe of the extreme lower Colorado River region grow it for the seed, which is used for food.

Panicum hirticaule subsp. stramineum (Hitchc. & Chase) Freckmann & Lelong

Culms 20-70 cm, robust, usually freely branching; nodes glabrous or sparsely hirsute, hairs papillose-based. Sheaths glabrous or sparsely hirsute, hairs papillose-based; blades 4-30 mm wide, glabrous or sparsely hirsute, hairs papillose-based, cordate, clasping basally. Panicles nodding. Spikelets 3.2-4 mm; lower paleas more than 1/2 as long as the upper florets. 2n = unknown.

Panicum hirticaule subsp. stramineum grows in rich bottomlands in southern Arizona, New Mexico, and western Mexico.

6.   Panicum mohavense Reeder
Mohave Witchgrass

Plants annual. Culms 2-8 cm, erect-spreading; nodes 1-2, hispid; internodes pilose, hairs papillose-based. Sheaths rounded, much longer than the internodes, with prominent veins, hispid, hairs papillose-based; ligules 0.2-0.4 mm, membranous, ciliate; blades 1-4 cm long, 1-3 mm wide, flat or involute apically, glabrous basally, margins ciliate, cilia papillose-based. Panicles congested, partially included in the sheaths, less than 1.5 times longer than wide; branches ascending, narrow; primary branches appressed to the main axes, secondary branches and pedicels attached to the distal 2/3; pedicels appressed, 1-2 mm. Spikelets 2-2.2 mm long, 1-1.3 mm wide, plump-ellipsoid, glabrous. Lower glumes 1.2-1.3 mm, acute to attenuate; upper glumes and lower lemmas 2-2.2 mm, 7-9-veined, apices purplish, acute; lower florets sterile; lower paleas 0.2-0.4 mm; upper florets 1.4-1.8 mm long, about 1 mm wide, broadly ovoid.

Panicum mohavense is known only from arid limestone terraces in Arizona and New Mexico.

7.   Panicum psilopodium Trin.

Plants annual; forming small clumps. Culms 20-60 cm tall, 0.8-1.2 mm thick, shortly decumbent to geniculate basally, erect distally; nodes glabrous; internodes glabrous. Sheaths shorter or longer than the internodes, rounded, smooth, glabrous; ligules about 1 mm; blades 5-15 cm long, 2-8 mm wide, flat, linear, glabrous or with a few marginal cilia near the base, bases contracted, apices long-acute. Panicles 10-20 cm long, 6-12 cm wide, exserted or partially included; primary branches alternate, ascending to strongly divergent, developing secondary branches in the basal 1/3-1/2; pedicels 4-9 mm, ascending. Spikelets 2.7-3.2 mm long, 1-1.2 mm wide, ovoid-ellipsoid, green tinged with purple, glaucous, glabrous, acute. Lower glumes 0.7-1.1 mm, about 2/5 as long as the spikelets, acute to attenuate; upper glumes and lower lemmas similar, equaling the spikelets, 11-13-veined, tapering to apiculate apices; lower paleas 1-2 mm; lower florets sterile; upper florets about 2.2 mm, ellipsoid, smooth, shiny, yellow at maturity, apices acute. 2n = 54.

Panicum psilopodium is native to eastern Asia. It has been reported from chrome ore piles in Canton, Maryland (Reed 1964), but no voucher specimens have been seen. In its native range it grows in open habitats, such as roadsides and waste places.

8.   Panicum capillarioides Vasey
Long-Beaked Witchgrass

Plants perennial; cespitose from a knotty crown, hirsute, hairs papillose-based or glabrous. Culms 30-75 cm tall, 1-2 mm thick, terete to slightly compressed, erect or ascending, stiff, often bent at the nodes, simple or sparingly branched; nodes densely pubescent. Sheaths shorter than or equaling the internodes, rounded, hirsute, green or tinged with purple, margins ciliate; ligules 0.5-1 mm; blades 12-30 cm long, 2-12 mm wide, stiffly erect or ascending, flat, pubescent, sometimes sparsely so, hairs papillose-based, bases truncate, apices attenuate. Panicles terminal, 15-30 cm long, 10-12(26) cm wide, usually shortly exserted, scarcely overtopping the blades; rachises hispid, sometimes glabrous basally; primary branches alternate or opposite, divergent, secondary branches divergent, most abundant on the distal 1/3 of the primary branches, with 1-3 spikelets; pedicels 2-20 mm, confined to the distal 1/3 of the branches; pulvini poorly developed, shortly pilose. Spikelets 5-6.5 mm long, 1-1.2 mm wide, glabrous, long-acuminate. Lower glumes 2-3 mm, about 1/2 as long as the spikelets, attached about 0.4 mm below the upper glumes, 5-7-veined, acute to obtuse; upper glumes and lower lemmas 5-6 mm, exceeding the upper florets by 3-4 mm, 9-13-veined; lower florets sterile; lower paleas 1.5-2 mm, acute; upper florets 1.6-2 mm long, 1-1.1 mm wide, smooth, chestnut brown when mature. 2n = 36.

Panicum capillarioides grows in sandy grasslands, oak savannahs, and rangelands, from southern Texas to northern Mexico.

9.   Panicum hirsutum Sw.
Giant Witchgrass

Plants perennial; forming large clumps from short rhizomes. Culms 100-300 cm tall, 4-10 mm thick, decumbent, semi-woody at the base, simple or branching from the middle nodes, prophylls prominent, to 15 cm; nodes contracted, pilose, sericeous; internodes glabrous or withpapillose-based hairs below the nodes. Sheaths shorter or longer than the internodes, rounded, sparsely hispid, hairs papillose-based, thick, fragile, penetrating and irritating the skin when handled, margins glabrous or ciliate; collars more densely pubescent than the sheaths, hairs papillose-based; ligules 1.5-2 mm, with longer hairs immediately behind, growing from the base of the blades; blades 20-50 cm long, 15-40 mm wide, spreading, flat or with involute margins, bases subcordate to cordate, margins glabrous or sparsely hairy. Panicles terminal, 25-45 cm long, 5-15 cm wide, lax, contracted to diffuse, not breaking at the base and becoming tumbleweeds, all or most secondary branches confined to the distal 1/3; lower branches whorled; pedicels 0.5-2 mm, appressed. Spikelets 1.8-2.5 mm long, 0.5-1 mm wide, narrowly ellipsoid, glabrous. Lower glumes 0.7-1.4 mm, about 1/2 as long as the spikelets, 3-5-veined, acute to attenuate; upper glumes and lower lemmas subequal, about as long as the spikelets, 7-11-veined; lower florets sterile; lower paleas 1.3-1.7 mm; upper florets 1.2-1.6 mm long, 0.5-0.7 mm wide, glabrous, smooth, shiny, chestnut brown to dark brown. 2n = 36.

Panicum hirsutum grows along river banks or in ditches, often among shrubs in partial shade. Its range extends from southern Texas through eastern Mexico, Central America, Cuba, and the West Indies to Ecuador, Brazil, and Argentina.

10.   Panicum bergii Arechav.
Berg's Witchgrass

Plants perennial; cespitose, with numerous leaves clustered at the base. Culms (10)50-140 cm, stout, stiffly erect, branched from the middle and lower nodes; lower nodes sericeous; lower internodes sericeous, hairs papillose-based, upper internodes sometimes glabrous. Sheaths rounded, glabrous or sparsely to densely hispid, hairs not fragile and prickly, not causing skin irritation, margins ciliate; ligules 1-3 mm; blades 3-60 cm long, 2-12 mm wide, flat or involute, ascending, adaxial surfaces densely hirsute basally, less densely so elsewhere, bases attenuate, apices acute. Panicles (4)15-40 cm long, (3)10-25 cm wide, about 1/3-1/2 as long as the plants, open, breaking at the base of the peduncles at maturity and dispersed as tumbleweeds, secondary branching mostly confined to the distal 1/3 of the primary branches; rachises densely hispid or glabrous; lower primary branches in whorls of 4-7, stiffly spreading, naked on the lower 1/2; pedicels 3-20 mm, appressed. Spikelets 2-3 mm long, 0.8-1.2 mm wide, glabrous. Lower glumes 1-1.6 mm, 5-veined, acuminate; upper glumes and lower lemmas similar, 2-2.8 mm, 7-9-veined, exceeding the upper florets by about 0.3 mm; lower florets sterile; lower paleas 1.4-2.2 mm; upper florets 1.5-1.9 mm long, 0.7-1 mm wide, smooth, chestnut brown at maturity. 2n = 36.

Panicum bergii is an eastern South American species that now grows in southeastern Texas. It occurs in ditches and shallow, sporadically flooded depressions in grasslands.

11.   Panicum diffusum Sw.
Spreading Witchgrass

Plants perennial; cespitose and shortly rhizomatous. Culms (6)25-100 cm, 0.5-3.5 mm thick, spreading to weakly ascending, usually freely branching; nodes pilose, hairs spreading to ascending; internodes pilose, with papillose-based hairs, or sparsely hispid. Sheaths rounded, glabrous, margins shortly ciliate distally; ligules 0.6-4 mm, of hairs; blades (3)6-15 cm long, 1-5 mm wide, spreading, abaxial surfaces sparsely hirsute, adaxial surfaces more densely so, hairs papillose-based, midribs prominent and not white, margins involute, bases cuneate, apices subulate. Terminal panicles 3-35 cm long, about 1/2 as wide, shortly exserted; axillary panicles smaller, not fully exserted; rachises scabridulous; primary branches usually solitary, sometimes paired, divergent and widely spaced, secondary branching mostly on the distal 1/3 of the primary branches; pedicels 1-4 mm, spreading to appressed, confined to the distal portions of the secondary branches. Spikelets 2.1-2.9 mm long, 0.8-1 mm wide, glabrous. Lower glumes 1-1.2 mm, to 1/2 as long as the spikelets, attenuate, 5-9-veined, veins anastomosing apically; upper glumes and lower lemmas similar, extending about 0.5 mm beyond the upper florets, 11-13-veined; lower florets sterile; lower paleas 1-1.3 mm; upper florets 1.5-1.8 mm long, 0.6-0.8 mm wide, smooth. 2n = 36.

Panicum diffusum grows along river banks, ditches, and disturbed areas in wet, loamy or clayey soils. Its range extends from Texas to the Caribbean and northern South America.

12.   Panicum ghiesbreghtii E. Fourn.
Ghiesbreght's Witchgrass

Plants perennial; cespitose. Culms 40-120 cm tall, 2-3 mm thick, decumbent to erect, branching from the base and the middle nodes; nodes pilose, hairs spreading; internodes hirsute, hairs papillose-based. Sheaths usually shorter than the internodes, hirsute, lower sheaths more so than those above, hairs papillose-based; collars densely pilose; ligules 0.5-4 mm; blades 16-55 cm long, 0.5-14 mm wide, erect to ascending, abaxial surfaces hirsute, hairs papillose-based, adaxial surfaces densely pilose, midveins prominent and whitish, bases truncate, margins ciliate basally, apices attenuate. Terminal panicles 7-35 cm long, 5-23 cm wide, about 1/2 as wide as long, shortly exserted or partially included, lax, open; axillary panicles smaller, included basally; primary branches diverging, lower branches solitary, upper branches solitary to subverticillate;secondary branching primarily in the distal 1/3; pedicels 1-4 mm, clavate, spreading to appressed. Spikelets 2.6-3.4 mm long, 0.9-1.2 mm wide, ovoid, glabrous. Lower glumes 1.4-1.7 mm, to 1/2 as long as the spikelets, acute, 5-7-veined; upper glumes and lower lemmas similar, exceeding the upper florets by 0.7-0.9 mm, 9-13-veined; lower florets sterile; lower paleas 0.5-1.3 mm; upper florets 1.7-2.3 mm long, 0.8-1.1 mm wide, smooth, ovoid. 2n = unknown.

Panicum ghiesbreghtii grows in low, moist ground, wet thickets, and savannahs, from southern Texas through Mexico, Central America, Cuba, and the West Indies to northern South America.

13.   Panicum hallii Vasey
Hall's Witchgrass

Plants perennial; cespitose. Culms 10-100 cm, 2-10 mm thick, erect, simple or sparingly branched basally; nodes sericeous, pilose or glabrous; internodes usually glaucous. Leaves often crowded basally; sheaths rounded, glabrous or hirsute, hairs fragile, papillose-based, margins sometimes ciliate distally; ligules 0.6-2 mm; blades 4-23 cm long, 1-10 mm wide, erect to spreading, flat or sometimes involute (on sterile branches), often curling at maturity, glaucous, abaxial surfaces sometimes with prominent papillae along the midribs, bases rounded or narrowing to the sheaths, margins cartilaginous, ciliate basally, scabridulous elsewhere, apices acute. Terminal panicles 7-31 cm long, 3-15 cm wide; rachises glabrous, tending to break at maturity; branches usually alternate, slender, stiff, ascending to divergent; pedicels 1-15 mm, appressed. Spikelets 2.1-4.2 mm long, 0.8-1 mm wide, usually ovoid, glabrous. Lower glumes 1.2-2.4 mm, 1/2-3/4 as long as the spikelets, attenuate; upper glumes and lower lemmas similar, 7-11-veined, acuminate, extending 0.3-1.2 mm beyond the upper florets; lower florets sterile; lower paleas 0.8-2 mm; upper florets 1.5-2.4 mm long, 0.7-1.2 mm wide, ovoid to ellipsoid, smooth, nigrescent. 2n = 18.

Panicum hallii grows on sandy, gravelly, or rocky land, including roadsides, pastures, rangeland, oak and pine savannahs, chaparral, and moist areas in deserts and on mesas. Its range extends from the southwestern United States to Guatemala.

Panicum hallii subsp. filipes (Scribn.) Freckmann & Lelong

Plants often taller than subsp. hallii, sparsely pubescent to almost glabrous. Blades relatively lax, ascending to spreading, not strongly clustered basally or curling at maturity. Panicles scarcely exceeding the blades, with more closely spaced spikelets than in subsp. hallii ; main branches rarely whorled, more crowded. Spikelets 2.1-3 mm.

Panicum hallii subsp. filipes often grows in moist soil. Its range extends from Arizona, Texas, and Louisiana to southern Mexico.

Panicum hallii Vasey subsp. hallii

Plants often depauperate, occasionally large, sparsely to moderately pubescent or hirsute. Blades usually erect or ascending, tending to arise from basal clumps and curl at maturity. Panicles usually greatly exceeding the blades, with a few spikelets; main branches solitary, ascending, well-separated. Spikelets 3-4.2 mm.

Panicum hallii subsp. hallii usually grows on drier sites than subsp. filipes. Its range extends from southern Colorado and Kansas to north central Mexico.

Panicum sect. Dichotomiflora (Hitchc.) Honda

Plants annual or perennial; cespitose, sometimes rhizomatous in the tropics. Culms erect to decumbent, compressed, sometimes slightly succulent. Sheaths almost glabrous or hispid, hairs papillose-based; ligules membranous, ciliate, cilia 2-4 mm. Panicles open or contracted; branches mostly solitary, stiff, naked basally; pedicels short, stiff, subappressed, prominently 3-angled, usually scabrous on the angles, widened and cuplike at the apices. Spikelets narrow, ellipsoid to lanceoloid, glabrous, pointed. Lower glumes 1/5-1/3 as long as the spikelets, clasping, 0-3-veined, truncate to subacute. Upper glumes and lower lemmas extending beyond the upper florets, 5-9-veined, veins prominent near the apices; lower florets sterile; lower paleas long and membranous to vestigial; upper florets smooth, shiny, glabrous.

Members of sect. Dichotomiflora usually grow in wet, open areas, some as emergents in shallow water. They are often found on disturbed ground. There are about seven species in the Western Hemisphere, but only three grow in the Flora region.

14.   Panicum lacustre Hitchc. & Ekman
Cypress-Swamp Panicum

Plants perennial; emergent aquatic or terrestrial, rooting at the lower nodes. Culms 100-150 cm, erect, succulent, with short innovations; nodes glabrous; internodes glabrous. Sheaths compressed, not keeled, overlapping but narrow, exposing the nodes, bladeless and glabrous or sparsely pilose below the water; ligules 1-2 mm, membranous, ciliate; blades 1-30 cm long, 2-4 mm wide, narrow, linear, flat or folded, abaxial surfaces sparsely pubescent, adaxial surfaces sparsely pilose. Panicles 10-30 cm, open, with many spikelets; primary branches fascicled at the base of the panicles, solitary and distant distally; pedicels 1-4 mm, sharply 3-angled, appressed. Spikelets 2-2.2 mm, glabrous. Lower glumes truncate to broadly triangular, 1/4 as long as the spikelets, 3-veined; lower paleas absent; upper glumes and lower lemmas equal, slightly exceeding the upper florets, 5- or 7-veined, pointed; lower florets sterile; upper florets relatively thin, smooth. 2n = unknown.

Panicum lacustre grows in shallow water or wet soil at the edge of cypress ponds in the Everglades of southern Florida. It also grows in Cuba.

15.   Panicum dichotomiflorum Michx.
Fall Panicum, Panic d'Automne

Plants annual or short-lived perennials in the Flora region, perennial in the tropics; usually terrestrial, sometimes aquatic but not floating. Culms 5-200 cm tall, 0.4-3 mm thick, decumbent to erect, commonly geniculate to ascending, rooting at the lower nodes when in water, simple to divergently branched from the lower and middle nodes, usually succulent, slightly compressed, glabrous; nodes usually swollen, sometimes constricted on robust plants, glabrous; internodes glabrous, shiny, pale green to purplish. Sheaths compressed, inflated, sparsely pubescent near the base, elsewhere mostly glabrous, sparsely pilose, or hispid, hairs sometimes papillose-based, margins or throat ciliate, with papillose-based hairs; ligules 0.5-2 mm; blades 10-65 cm long, 3-25 mm wide, glabrous or sparsely pilose, often scabrous near the margins, midribs stout, whitish. Panicles 4-40 cm, diffuse, lax, with a few spikelets; branches to 15 cm, alternate or opposite, occasionally verticillate, ascending to spreading, stiff, scabrous; pedicels 1-6 mm, sharply 3-angled, scabrous, expanded to cuplike apices, appressed mostly to the abaxial side of the branches. Spikelets 1.8-3.8 mm long, 0.7-1.2 mm wide, ellipsoid to narrowly ovoid, light green to red-purple, glabrous, acute to acuminate. Lower glumes 0.6-1.2 mm, 1/4-1/3 as long as the spikelets, 0-3-veined, obtuse to acute; upper glumes and lower lemmas similar, exceeding the upper florets by 0.3-0.6 mm, 7-9-veined; lower paleas vestigial to almost as long as the lower lemmas; lower florets sterile; upper florets 1.4-2.5 mm long, 0.7-1.1 mm wide, narrowly ellipsoid, smooth, shiny, stramineous to nigrescent, with pale veins. 2n = 36, 54.

Panicum dichotomiflorum grows in open, often wet, disturbed areas such as cultivated and fallow fields, roadsides, ditches, open stream banks, receding shores, clearings in flood plain woods, and sometimes in shallow water. It is probably native throughout the eastern United States and adjacent Canada, but introduced elsewhere, including in the western United States. Its size and habit may be partly under genetic control, but these features also seem to be strongly affected by moisture levels, soil richness, competition, and the time of germination.

Panicum dichotomiflorum subsp. bartowense (Scribn. & Merr.) Freckmann & Lelong

Culms often 100-200 cm, stout, erect, simple or sparingly branched. Sheaths loosely overlapping, prominently hispid, hairs papillose-based. Pedicels usually less than 3 mm and shorter than the spikelets. Spikelets 2.3-2.8 mm, tapered from below the middle to the acuminate apices; upper glumes and lower lemmas subcoriaceous.

Panicum dichotomiflorum subsp. bartowense grows in Florida, Cuba, and the Bahamas. Reports from more northerly areas may represent introductions or misidentifications.

Panicum dichotomiflorum Michx. subsp. dichotomiflorum
Panic d'Automne Dressé

Culms 5-200 cm. Sheaths glabrous or sparsely pilose, not hispid with papillose-based hairs. Pedicels usually less than 3 mm and shorter than the spikelets. Spikelets 2.3-3.8 mm, tapered from below the middle to the acuminate apices; upper glumes and lower lemmas subcoriaceous.

Panicum dichotomiflorum subsp. dichotomiflorum is the most common of the three subspecies and is found throughout the range of the species. In the past, members of this subspecies have been treated as two different taxa, var. geniculatum (Alph. Wood) Fernald and var. dichotomiflorum, with more erect, slender plants having fewer long-exserted panicles with slender, ascending branches and less crowded spikelets being placed in var. dichotomiflorum. Such plants are more common in the southern part of the subspeciesrange, but the traits are poorly correlated and the differences are at least in part affected by photoperiod, nighttime temperatures, and the time of seed germination.

Panicum dichotomiflorum subsp. puritanorum (Svenson) Freckmann & Lelong

Culms 30-60 cm, usually slender, sometimes to 2 mm thick. Sheaths glabrous or sparsely pilose, hairs not papillose-based. Pedicels often over 3 mm, usually longer than the spikelets. Spikelets 1.8-2.2 mm, widest at about the middle, acute. Upper glumes and lower lemmas slightly exceeding the upper florets, submembranaceous.

Panicum dichotomiflorum subsp. puritanorum has a sporadic distribution on receding shores along the Atlantic coast from Nova Scotia to Virginia, and around southern Lake Michigan. The small spikelets with thin glumes and thin lower lemmas are probably genetically fixed traits; the commonly delicate habit, however, probably results from late season seed germination following receding water.

16.   Panicum paludosum Roxb.
Aquatic Panicum

Plants perennial;more or less cespitose, rhizomatous or stoloniferous, free-floating or rooting in shallow water. Culms 30-150 cm tall, 3-7 mm thick, compressed, spongy, glabrous, decumbent and rooting at the lower nodes in shallow water; nodes glabrous; internodes glabrous, smooth. Sheaths usually shorter than the internodes, not keeled, glabrous or sparsely hispid distally; ligules 1-4 mm; blades 10-40 cm long, 5-15 mm wide, flat, glabrous, contracted basally, attenuate distally, apices acute. Panicles 10-25 cm long, 5-17 cm wide, shortly exserted or included basally; primary branches 4-12 cm, ascending to spreading, secondary and higher order branches confined to the distal 2/3; pedicels 1-4 mm, sharply 3-angled, ascending to appressed. Spikelets 3-4 mm long, 0.8-2 mm wide, lanceolate. Lower glumes 0.5-0.9 mm, 1/5-1/3 as long as the spikelets, rounded, glabrous, truncate, weakly 1-3-veined; upper glumes and lemmas subequal, glabrous, 9-11-veined, veins prominent, apices acute to acuminate; lower paleas about 2/3 as long as the lower lemmas; lower florets sterile; upper florets 2-2.7 mm, narrowly ellipsoid, smooth, shiny, yellowish. 2n = 54.

Panicum paludosum is an Asian species that grows in shallow water. It has been found in Baltimore, Maryland, but may not be established there.

Panicum sect. Repentia Stapf

Plants perennial; rhizomatous, rhizomes long or short, sometimes with scalelike leaves, sometime forming a compact, knotty base. Culms 20-300 cm, erect, firm, terete, often glaucous. Sheaths glabrous or pilose; ligules 0.5-6 mm, membranous, ciliate; blades linear (sometimes involute), firm. Panicles open or contracted. Spikelets lanceoloid, glabrous, acute to acuminate. Lower glumes about 1/4-2/3 as long as the spikelets, 1-7-veined, usually acute or truncate, sometimes acuminate; upper glumes and lower lemmas unequal, stiffly pointed, upper glumes often exceeding the lower lemmas, the two often separating (gaping) beyond the florets; lower florets staminate; lower paleas well-developed; upper florets smooth, shiny, often pointed.

There are approximately 12 species of Panicum sect. Repentia in the Western Hemisphere, four of which grow in the Flora region. The species generally inhabit wet sites, growing on coastal dunes, sea beaches or along the margins of rivers.

17.   Panicum repens L.
Torpedo Grass

Plants perennial; rhizomatous, forming extensive colonies, rhizomes long, to 5 mm thick, branching, scaly, sharply pointed. Culms 20-90 cm tall, 1.8-2.8 mm thick, erect, rigid, simple or branching from the lower and middle nodes; nodes glabrous or sparsely hispid; internodes glabrous. Sheaths generally shorter than the internodes, not keeled, lower nodes glabrous or hispid, hairs papillose-based, particularly near the summits; ligules 0.5-1 mm; blades 3-25 cm long, 2-8 mm wide, often distichous, flat to slightly involute, firm, adaxial surfaces pilose basally, glabrous or sparsely pubescent abaxially. Panicles 3-24 cm long, usually less than 5 cm wide, open; primary branches 2-11 cm, alternate, few, stiffly ascending to spreading; pedicels 1-6 mm, subappressed. Spikelets 2.2-2.8 mm long, 0.8-1.3 mm wide, ellipsoid-ovoid, pale green, acute, upper glumes and lower lemmas sometimes separating (gaping) beyond the florets. Lower glumes 0.5-1 mm, 1/5-2/5 as long as the spikelets, glabrous, faintly 1-5-veined, subtruncate to broadly acute; upper glumes and lower lemmas glabrous, extending 0.1-0.5 mm beyond the upper florets, scarcely separated; upper glumes 7-11-veined, shorter than the lower lemmas, acute to short-acuminate; lower florets staminate; lower lemmas 7-11-veined; lower paleas 1.9-2.1 mm, oblong; upper florets 1.8-2.7 mm long, 0.7-1.3 mm wide, broadly ellipsoid, broadest at or above the middle, glabrous, shiny, smooth, apices rounded. 2n = 36, 40, 45, 54.

Panicum repens grows on open, moist, sandy beaches and the shores of lakes and ponds, occasionally extending out into or onto the water. It is mostly, but not exclusively, coastal. It grows on tropical and subtropical coasts throughout the world and may have been introduced to the Americas from elsewhere. Small plants having small, dense panicles of purplish spikelets with longer, subacute lower glumes have been named Panicum gouinii E. Fourn., but they intergrade with more typical plants and do not seem to merit taxonomic recognition.

18.   Panicum coloratum L.
Kleingrass

Plants perennial; cespitose, usually with short, knotty rhizomes. Culms 50-140 cm tall, 1.5-2.5 mm thick, usually erect, rarely decumbent, firm; nodes glabrous or puberulent; internodes glabrous. Sheaths shorter than the internodes, glabrous or hispid, hairs papillose-based, rounded basally; ligules 0.5-2 mm; blades 10-30 cm long, 2-8 mm wide, flat, glabrous or sparsely hirsute on 1 or both surfaces. Panicles 4-25(40) cm long, 3-14 cm wide, exserted, lax; primary branches 3-14 cm, opposite and alternate, ascending, glabrous, branching in the distal 2/3; pedicels 1-4 mm, appressed or spreading. Spikelets 2.5-3.5 mm long, 1-1.2 mm wide, narrowly ovoid to ellipsoid, glabrous, acute. Lower glumes 1-1.5 mm, about 1/3 as long as the spikelets, glabrous, 1-3-veined, acute; upper glumes slightly exceeding the lower lemmas, glabrous, acute, scarcely separated from the lower lemmas; lower florets staminate; lower lemmas similar to the upper glumes; lower paleas 2-3 mm, oblong; upper florets 2-2.5 mm long, 0.8-1 mm wide, ellipsoid, widest below the middle, glabrous, smooth, shiny, apices lightly beaked. 2n = 18, 36, 41, 42, 43, 45, 54, 63 (United States material apparently usually tetraploid, with 2n = 36).

Panicum coloratum is an African species that has been widely introduced into tropical and subtropical regions around the world. It is now established in the Flora region, growing in open, usually wet ground; it is also occasionally cultivated as a forage grass.

19.   Panicum amarum Elliott
Bitter Beachgrass

Plants perennial; rhizomatous, rhizomes stout, glabrous and glaucous throughout. Culms 20-250 cm tall, 3-10 mm thick, erect or decumbent, simple or branched from the lower nodes; nodes glabrous; internodes glabrous, glaucous. Sheaths shorter or longer than the internodes, not keeled, glabrous; collars often glaucous and purplish; ligules 1-5 mm; blades 7-50 cm long, 2-13 mm wide, erect or ascending, firm, thick, flat basally, more or less involute towards the apices. Panicles 10-80 cm long, 2-17 cm wide, contracted, slightly nodding; primary branches whorled or opposite, strongly ascending to appressed; pedicels 0.5-15 mm, appressed to slightly divergent. Spikelets 4-7.7 mm long, 1.5-2 mm wide, narrowly ovoid, glabrous, acuminate; lower florets staminate. Glumes and lower lemmas relatively thick; lower glumes 2.8-4 mm, 1/2-4/5 as long as the spikelets, 3-9-veined, apices of the midveins sometimes scabridulous; upper glumes and lower lemmas extending 1.5-3 mm beyond the upper florets, apices stiffly gaping; upper glumes 3.9-7.6 mm, 5-9-veined; lower lemmas slightly shorter than the upper glumes, 7-9-veined, lower paleas 3-7 mm, oblong-hastate, folded over the anthers; lower florets staminate; upper florets 2.4-3.9 mm long, 1-1.8 mm wide, narrowly ovoid to oblong, glabrous, smooth, shiny, lemma margins clasping the paleas only at the base. 2n = 36, 54.

Panicum amarum grows in the coastal dunes, wet sandy soils, and the margins of swamps, along the Atlantic Ocean and the Gulf of Mexico from Connecticut to northeastern Mexico. It is also known, as an introduction, from a few inland locations in New Mexico, North Carolina, and West Virginia, as well as in the Bahamas and Cuba.

Panicum amarum subsp. amarulum (Hitchc. & Chase) Freckmann & Lelong

Plants with short (usually) or ascending rhizomes. Culms usually 100-250 cm, robust, decumbent, densely bunched (occasionally with more elongated rhizomes and less bunching in the southern part of its range). Panicles usually more than 5 cm wide, spikelet density high; primary branches usually 2 or more per node, smooth to moderately scabrous, usually with quaternary branching. Spikelets 4-5.9 mm; lower glumes 3-5-veined, veins less evident than in subsp. amarum, midvein smooth distally.

Panicum amarum subsp. amarulum grows in swales behind the first dune and on sandy borders of wet areas. It extends as far north as northern New Jersey and extends southward into Mexico. It has been introduced to Massachusetts, West Virginia, Cuba, and the Bahamas. Panicum amarum subsp. amarulum is a fertile tetraploid, and possibly a progenitor of subsp. amarum, with which it intergrades in the Gulf region. Plants that intergrade with P. virgatum are evident in some coastal areas; they may represent hybrids.

Panicum amarum Elliott subsp. amarum

Plants with horizontally elongated rhizomes, internodes mostly over 1 cm, scales not overlapping. Culms 20-150 cm, solitary and erect or somewhat bunched and decumbent at the base, often branching from the lower nodes. Panicles often less than 5 cm wide, spikelet density less than in subsp. amarulum ; primary branches solitary or paired, often strongly scabrous, with secondary and tertiary branches. Spikelets 4.7-7.7 mm. Lower glumes with 7-9 prominent veins, midvein scabridulous distally.

Panicum amarum subsp. amarum grows on foredunes, where its longer rhizomes probably permit it to respond quickly to being buried under shifting sand, and occasionally in the swales with subsp. amarulum. It ranges farther north (into Connecticut) than subsp. amarulum, but apparently not into Mexico, Cuba, or the Bahamas. It includes both tetraploids and hexaploids, and is partially sterile. Hybridization with P. virgatum may have had some role in its origin.

20.   Panicum virgatum L.
Switchgrass, Panic Raide

Plants perennial; rhizomatous, rhizomes often loosely interwoven, hard, with closely overlapping scales, sometimes short or forming a knotty crown. Culms 40-300 cm tall, 3-5 mm thick, solitary or forming dense clumps, erect or decumbent, usually simple; nodes glabrous; internodes hard, glabrous or glaucous, green or purplish. Sheaths longer than the lower internodes, shorter than those above, glabrous or pilose, especially on the throat, margins usually ciliate; ligules 2-6 mm; blades 10-60 cm long, 2-15 mm wide, flat, erect, ascending or spreading, glabrous or pubescent, adaxial surfaces sometimes densely pubescent, particularly basally, bases rounded to slightly narrowed, margins scabrous. Panicles 10-55 cm long, 4-20 cm wide, exserted, open; primary branches thin, straight, solitary to whorled or fascicled, ascending to spreading, scabrous, usually rebranching once; pedicels 0.5-20 mm, appressed to spreading. Spikelets 2.5-8 mm long, 1.2-2.5 mm wide, narrowly lanceoloid, turgid to slightly laterally compressed, glabrous, acuminate. Lower glumes 1.8-3.2 mm, 1/2-4/5 as long as the spikelets, glabrous, 5-9-veined, acuminate; upper glumes and lower lemmas extending 0.4-3 mm beyond the upper florets, 7-11-veined, strongly gaping at the apices; lower florets staminate; lower paleas 3-3.5 mm, ovate-hastate, lateral lobes folded over the anthers before anthesis; upper florets 2.3-3 mm long, 0.8-1.1 mm wide, narrowly ovoid, smooth, glabrous, shiny; upper lemmas clasping the paleas only at the base. 2n = 18, 21, 25, 30, 32, 35, 36, 54-60, 67-72, 74, 77, 90, 108.

Panicum virgatum grows in tallgrass prairies, especially mesic to wet types where it is a major component of the vegetation, and on dry slopes, sand, open oak or pine woodlands, shores, river banks, and brackish marshes. Its range extends, primarily on the eastern side of the Rocky Mountains, from southern Canada through the United States to Mexico, Cuba, Bermuda, and Costa Rica, and, possibly as an introduction, in Argentina. It has also been introduced as a forage grass to other parts of the world.

Panicum virgatum is an important and palatable forage grass, but its abundance in native grasslands decreases with grazing. Several types are planted for range and wildlife habitat improvement. Plants from eastern New Mexico, western Texas, and northern Mexico tend to have larger spikelets (6-8 mm versus 2.5-5.5 mm) and are sometimes called P. havardii Vasey.

Tetraploids appear to be the most common ploidy level, especially in the upper midwest and northern plains, with higher ploidy levels being more common southwards, but plants in a small area can range from diploid through duodecaploid, with dysploid derivatives. If morphological markers matched chromosome numbers and ecotypic characters, the species could be considered an aggregate of numerous microspecies. In the absence of such correlations, it must be regarded as simply a wide-ranging, highly variable taxon. Plants identified as Panicum virgatum var. cubense Griseb. and P. virgatum var. spissum Linder represent end points of geographic clines.

Panicum virgatum is not always readily separable from P. amarum, particularly P. amarum subsp. amarulum; future work may support their treatment as conspecific subspecies.

Panicum sect. Urvilleana (Hitchc. & Chase) Pilg.

Plants perennial; rhizomatous, rhizomes stout, horizontal or vertical. Culms erect, arising in tufts or solitary. Ligules membranous, ciliate. Panicles narrow to lax; branches ascending to spreading; secondary branches and pedicels short, crowded, often appressed. Spikelets ovoid, densely to sparsely villous, hairs silvery or tawny-white, apices acute. Lower glumes about 3/4 as long as the spikelets, (5)7-9(11)-veined; upper glumes and lower lemmas 7-15-veined; lower florets staminate; lower paleas as large as the lower lemmas; upper lemmas villous on the basal portion of the margins.

Panicum sect. Urvilleana consists of three species growing on coastal dunes and sand in South America. There is one species in the Flora region.

21.   Panicum urvilleanum Kunth
Silky Panicgrass

Plants perennial. Culms 50-100 cm, erect, solitary or in small tufts from stout, scaly, creeping to vertical rhizomes or stolons, simple or branching at the base; nodes densely villous. Sheaths densely villous; ligules membranous, ciliate, hairs 1.5-2 mm; blades 20-60 cm long, 4-10 mm wide, ascending to spreading, strigose to subglabrous, flat basally, tapering to a long, involute point. Panicles 20-30 cm long, 3-9 cm wide, narrow, shortly exserted; branches slender, ascending; secondary branches and pedicels 1-4 mm, crowded, ascending to appressed. Spikelets 5-7 mm, densely villous, hairs silvery or tawny-white. Lower glumes about 3/4 the length of the spikelets, 7-11-veined; upper glumes and lower lemmas 7-15-veined; lower florets staminate; lower paleas about as long as the lower lemmas; upper florets striate, margins of the upper lemmas villous, hairs white; lodicules very large. 2n = 36.

Panicum urvilleanum grows on desert sand dunes and in creosote bush scrubland in the Mojave and Colorado desert regions of southern California, southern Nevada, and western Arizona. It also grows in Peru, Chile, and Argentina.

Panicum subg. Agrostoidea (Nash) Zuloaga

Plants perennial; usually cespitose, often from scaly rhizomes. Culms often compressed. Sheaths often keeled; ligules membranous, papery, often erose, usually ciliate; blades with vascular bundles surrounded by a single Kranz sheath with centrifugal chloroplasts and separated by 2-3 isodiametric mesophyll cells; chloroplasts without well-developed grana. Photosynthesis of the C₄ NADP-me type. Panicles contracted to lax, usually with many spikelets; secondary branches usually present; pedicels short. Spikelets ovoid to ellipsoid, glabrous. Lower glumes varying in length, 0-3-veined (rarely 7-veined); upper glumes and lower lemmas usually 3-5-veined (rarely 7-11-veined); lower florets usually sterile, occasionally staminate; lower paleas absent, small, or large, not thickened; upper florets variable. x = 9 or 10.

Panicum subg. Agrostoidea is found primarily in warm temperate to tropical regions of the New World, extending from the southern United States through South America. One section is native to India. Species of subg. Agrostoidea usually grow in open but mesic places, such as the edges of streams, rivers, ponds, and wet meadows.

Panicum sect. Agrostoidea (Nash) C.C. Hsu

Plants perennial; cespitose. Culms soft, somewhat compressed. Ligules membranous, papery, often erose, with or without cilia. Panicles open to contracted, with many, more or less appressed spikelets; branches narrow, nearly simple; pedicels 0.1-3 mm, crowded, somewhat secund. Spikelets long-ellipsoid, acute. Lower glumes 1/3-2/3 as long as the spikelets, 3-veined; upper glumes and lower lemmas 5-veined, strongly keeled along the midveins; lower florets sterile; lower paleas small; upper florets smooth, shiny, with an apical tuft of prickly hairs. x = 9.

Panicum sect. Agrostoidea includes about four species, one of which is found in the Flora region.

22.   Panicum rigidulum Bosc ex Nees
Redtop Panicum

Plants perennial; cespitose, not rhizomatous, occasionally purple-tinged throughout, mostly glabrous throughout (except as noted). Culms 35-150 cm, stout, compressed. Sheaths more or less strongly compressed or keeled, sides usually glabrous or sparsely pubescent distally; ligules 0.3-3 mm, membranous, erose or ciliate, cilia often themselves fimbriate; blades 8-50 cm long, 2-12 mm wide, flat or folded, both surfaces usually glabrous or scabridulous, or the adaxial surfaces sparsely pilose basally. Panicles terminal and axillary, 9-40 cm, 1/3-3/4 as wide as long, usually dense; ultimate branchlets usually appressed, 1-sided, scabridulous; pedicels 0.5-1.5 mm, usually appressed, sometimes with 1-several slender hairs at the apices. Spikelets usually 1.6-3.8 mm, usually subsessile, lanceolate, green, purple-tinged, or purple, glabrous. Lower glumes 2/5-3/4 as long as the spikelets, 3-veined, midveins keeled; upper glumes and lower lemmas subequal or the glumes slightly longer, often spreading slightly apart at the apices, midveins keeled, usually scabridulous apically; lower florets sterile; lower paleas to 2/3 as long as the lower lemmas; upper florets 1.4-2 mm long, 0.6-0.8 mm wide, 2/5-3/4 as long as the spikelets, occasionally stipitate, lustrous, with a tuft of minute, thickish hairs at the apices; upper lemmas thick, stiff, clasping the upper paleas throughout their length. 2n = 18.

Panicum rigidulum grows in swamps, wet woodlands, flood-plain forests, wet pine savannahs, marshy shores of rivers, ponds, and lakes, drainage ditches, and other similar wet to moist places; it is rarely found in dry sites. Its range extends from southern Canada to Mexico, Guatemala, and the Antilles.

Panicum rigidulum subsp. abscissum (Swallen) Freckmann & Lelong

Plants yellowish-green. Culms compressed, densely cespitose. Sheaths strongly keeled, 3-6 mm wide from the keel to the margins, truncate or broadly auriculate, occasionally ciliate distally; ligules minute, membranous; blades 0.7-1.5 mm wide from the blunt keel to the margins, to 2.5 mm wide overall, thick, curved or flexuous, rigid, glabrousor scabridulous on both surfaces and along the margins, bases much narrower than the subtending sheaths, margins often sparsely ciliate, with long, slender hairs near the base. Panicles slender, purplish, long-exserted; branches few, appressed or ascending, with relatively few spikelets. Spikelets 2.4-2.8(3) mm, purplish, glabrous, obliquely set on the pedicels, mostly abortive. Lower glumes 1.6-2 mm, often divergent; upper glumes and lower lemmas subequal, often spreading apart.

Panicum rigidulum subsp. abscissum is endemic to central Florida. It usually grows in marshy, sandy ground, but is occasionally found in dry, sandy sites (e.g., the type specimen, collected near Lake Sebring).

Panicum rigidulum subsp. abscissum is very similar vegetatively and reproductively to subsp. pubescens and subsp. combsii. Its spikelets also suggest those of P. virgatum.

Panicum rigidulum subsp. combsii (Scribn. & C.R. Ball) Freckmann & Lelong

Plants similar to subsp. pubescens, but often shortly rhizomatous, more nearly glabrous, and more deeply and consistently purple throughout. Ligules nearly obsolete; blades usually 2-7 mm wide, often folded or involute, usually pilose adaxially, at least near the base, bases about equal in width to the subtending sheaths. Spikelets 2.6-3.8 mm, usually purple, slender, erect on the pedicels. Lower glumes to 3/4 as long as the spikelets.

Panicum rigidulum subsp. combsii occurs in the same moist habitats as subsp. pubescens, but is much less common. Its long, narrow, purple, often gaping spikelets somewhat resemble those of P. virgatum, which often grows in the same habitats.

Panicum rigidulum subsp. elongatum (Scribn.) Freckmann & Lelong

Plants similar to subsp. rigidulum, but more conspicuously purple-tinged throughout, especially the panicles. Ligules 0.3-1 mm, membranous; blades usually 5-12 mm wide, flat, mostly glabrous or scabridulous, bases about equal in width to the subtending sheaths. Panicles relatively narrow; branches few, stiffly ascending. Spikelets 2.4-3 mm long, usually less than 0.6 mm wide, conspicuously stipitate, purple, often falcate, subsecund along the branchlets. Upper florets stipitate, stipes to 0.4 mm, slender.

Panicum rigidulum subsp. elongatum is most common in the piedmont and mountain regions of the eastern United States.

Panicum rigidulum subsp. pubescens (Vasey) Freckmann & Lelong

Culms less than 100 cm, usually slender, greatly compressed. Leaves mostly basal; sheaths narrower than those of subspp. elongatum and rigidulum, compressed, often pubescent, at least along the sides near the summit or at the throat; ligules 0.5-3 mm, membranous, usually fimbriate-ciliate; blades usually 2-7 mm wide, often folded or involute, usually pilose adaxially, at least near the base, bases about equal in width to the subtending sheaths. Panicles mostly terminal. Spikelets 2-2.7 mm, green or slightly purplish, set obliquely on the pedicels. Lower glumes about 1/2 as long as the spikelets; upper glumes slightly longer than the lower lemmas, acute; lower lemmas acute, the apices diverging slightly from those of the upper glumes.

Panicum rigidulum subsp. pubescens grows primarily in moist pine savannahs, bogs, and other similar open, sandy habitats on the Atlantic and Gulf coastal plains.

Panicum rigidulum Bosc ex Nees subsp. rigidulum

Culms 40-150 cm, rather robust. Sheaths with the throat usually glabrous or sparsely pilose on the sides; ligules 0.3-1 mm, membranous; blades usually 5-12 mm wide, flat, mostly glabrous or scabridulous, bases about equal in width to the subtending sheaths. Panicles terminal and axillary, usually with many spikelets. Spikelets 1.6-2.5 mm long, usually over 0.6 mm wide, crowded, green or purplish-tinged, pedicellate, pedicels short, with 1-several slender hairs near the apices.

Panicum rigidulum subsp. rigidulum is the most common, most variable, and widest ranging of the five subspecies.

23.   Panicum anceps Michx.
Beaked Panicgrass

Plants perennial; conspicuously rhizomatous, rhizomes short or elongate, stout, scaly. Culms 30-130 cm, terete to slightly compressed. Sheaths laterally compressed, glabrous or sparsely to densely pilose or villous, especially at the summit; ligules less than 0.5 mm, membranous, erose, often brownish; blades 10-50 cm long, 4-12 mm wide, erect, adaxial surfaces pilose at least basally, glabrous or pilose abaxially. Panicles 10-40 cm, 1/4-2/3 as wide as long, well-exserted at anthesis; branches relatively few, stiffly spreading or ascending; ultimate branchlets 1-sided; pedicels 0.1-3 mm, scabridulous to scabrous, appressed. Spikelets 2.3-3.9 mm, narrowly ellipsoid to ovoid, usually subsessile, usually pale to yellowish-green, glabrous, often falcate and gaping at the apices, rarely lanceolate, densely crowded on short, appressed branchlets, set obliquely on short pedicels. Lower glumes 1/3-1/2 as long as the spikelets, 3-veined, keels scabrous, apices acute; upper glumes and lower lemmas subequal, keeled, beaked, usually gaping at the apices; lower florets sterile; lower paleas subequal to the lower lemmas; upper florets 1.5-2.2 mm long, about 1 mm wide, 2/5-3/4 as long as the spikelets, apices with a tuft of minute, thick hairs; upper lemmas thick, stiff, clasping the upper paleas throughout their length. 2n = 18, 36.

Panicum anceps grows in low, moist, primarily sandy areas, pine savannahs, the borders of flood-plain swamps, mesic woodlands, roadsides, and upland pine-hardwood forests. It is restricted to the United States.

Panicum anceps Michx. subsp. anceps

Plants rhizomatous, rhizomes relatively short and stout. Panicles primarily terminal; primary branches usually few, stiffly ascending, with short branchlets and crowded, subsecund spikelets on short pedicels. Spikelets 2.7-3.9 mm, often lanceolate, falcate, with prominent green veins, acuminate.

Panicum anceps subsp. anceps is widespread in all physiographic provinces within its range.

Panicum anceps subsp. rhizomatum (Hitchc. & Chase) Freckmann & Lelong

Plants rhizomatous, rhizomes relatively long and slender. Panicles terminal and axillary; branches more numerous, appressed, congested, with dense clusters of spikelets. Spikelets 2.3-2.8 mm, not clearly falcate, often ovoid-lanceolate, purplish-stained, acute.

Panicum anceps subsp. rhizomatum grows in the Atlantic and Gulf coastal plains.

The small, crowded, often purplish spikelets of this subspecies often closely resemble those of Panicum rigidulum.

Panicum sect. Tenera (Hitchc. & Chase) Pilg.

Plants perennial; cespitose. Culms wiry, somewhat compressed, erect. Ligules less than 0.4 mm, membranous. Panicles narrow, with a few spikelets; branches appressed; pedicels short, with a few long hairs at the apices. Lower glumes 1- or 3-veined; lower florets sterile; lower paleas small; upper florets smooth, shiny. x = 10.

24.   Panicum tenerum Beyr. ex Trin.
Blue-Joint Panicgrass

Plants perennial; cespitose, with short, knotted rhizomes. Culms 40-100 cm, erect, simple or branching from the lower nodes; nodes glabrous; internodes glabrous. Sheaths shorter than the internodes, usually glabrous, lower sheaths sometimes pilose at the summit, hairs papillose-based; ligules 0.1-0.4 mm; blades 4-19 cm long, 1.5-4 mm wide, mostly involute at maturity, erect, firm, abaxial surfaces usually glabrous, adaxial surfaces often sparsely pilose, particularly basally. Panicles 3-12 cm long, less than 1 cm wide, contracted, with few spikelets; branches 1-4 cm, few, ascending-appressed; ultimate branchlets 1-sided; pedicels 0.5-3 mm, scabridulous, appressed, usually with a few slender hairs at the apices. Spikelets 1.8-2.8 mm long, 0.8-1 mm wide, usually subsessile, lanceoloid to narrowly ovoid, green, often purplish-stained, glabrous, acute. Lower glumes 0.9-3 mm, 1/2-2/3 as long as the spikelets, 1-3-veined, not keeled over the midveins, acute or obtuse; upper glumes and lower lemmas subequal, 5-7-veined, midveins not keeled, acute to short-acuminate, occasionally gaping at the apices; lower florets sterile; lower paleas about 1/2-2/3 as long as the lower lemmas; upper florets 1.1-1.8 mm long, 0.6-0.8 mm wide, 2/5-3/4 as long as the spikelets, lustrous, usually brownish, apices glabrous; upper lemmas thick, stiff, clasping the upper paleas throughout their length. 2n = 20.

Panicum tenerum grows in wet or moist, sandy (often peaty) soil, depressions in pine savannahs, bogs, marshes, pond margins, and interdunal swales. Its range includes the Atlantic and Gulf coastal plains of the United States, the Antilles, Bahamas, and Central America. Panicum tenerum exhibits numerous features of the widespread and polymorphic Panicum rigidulum, particularly P. rigidulum subsp. pubescens.

Panicum obtusum: See Hopia

Panicum sect. Bulbosum Zuloaga: See Zuloagaea

Panicum sect. Antidotalia Freckmann & Lelong

Plants perennial; rhizomatous. Culms robust, lignified, branching at the middle nodes. Ligules membranous, ciliate, cilia longer than the membranous base. Panicles pyramidal, more or less lax, with many spikelets. Spikelets ellipsoid to ovoid. Lower glumes to 1/2 as long as the spikelets, 1-5-veined; upper glumes and lower lemmas 7-11-veined; lower florets staminate; upper florets smooth, shiny. x = 9.

In Panicum sect. Antidotalia, the culms become almost woody at maturity; even a hammer blow fails to flatten them.

28.   Panicum antidotale Retz.
Blue Panicgrass

Plants perennial; cespitose, rhizomatous, rhizomes about 1 cm thick, knotted, pubescent, with large, scalelike leaves. Culms 50-300 cm tall, 2-4 mm thick, often compressed, erect or ascending, hard, becoming almost woody; nodes swollen, glabrous or pubescent; internodes glabrous, glaucous. Sheaths not keeled, shorter than or equal to the internodes, glabrous or the lower sheaths at least partially pubescent, hairs papillose-based; ligules 0.3-1.5 mm; blades 10-60 cm long, 3-20 mm wide, elongate, flat, abaxial surfaces and margins scabrous, adaxial surfaces occasionally pubescent near the base, with prominent, white midveins, bases rounded to narrowed. Panicles 10-45 cm, to 1/2 as wide as long, open or somewhat contracted, with many spikelets; branches 4-12 cm, opposite or alternate, ascending to spreading; pedicels 0.3-2.5 mm, scabridulous to scabrous, appressed to diverging less than 45° from the branch axes. Spikelets 2.4-3.4 mm long, 1-1.3 mm wide, ellipsoid-lanceoloid to narrowly ovoid, often purplish, glabrous, acute. Lower glumes 1.4-2.2 mm, 1/3-1/2 as long as the spikelets, 3-5-veined, obtuse; upper glumes and lower lemmas subequal, glabrous, 5-9-veined, margins scarious, acute; lower florets staminate; upper florets 1.8-2.8 mm long, 0.9-1.1 mm wide, smooth, lustrous, acute. 2n = 18, 36.

Panicum antidotale is native to India. It is grown in the Flora region as a forage grass, primarily in the southwestern United States. It is now established in the region, being found in open, disturbed areas and fields.

Panicum sect. Hemitoma (Hitchc.) Freckmann & Lelong

Plants perennial; aquatic or semi-aquatic, rhizomatous, rhizomes extensive. Culms erect or sprawling, often sterile. Ligules membranous and ciliate, or lacerate. Panicles narrow; branches few, spikelike, erect; ultimate branchlets 1-sided; pedicels less than 2 mm long, appressed. Spikelets lanceoloid, laterally compressed, glabrous; lower florets staminate; upper lemmas thin, flexible, whitish, clasping the paleas only near the base. x = 9.

29.   Panicum hemitomon Schult.
Maidencane

Plants perennial; robust, aquatic or semi-aquatic, forming extensive colonies through spreading rhizomes. Culms 50-200 cm, mostly erect and sterile, glabrous, often rooting from the lower nodes if submerged. Sheaths usually glabrous, or pilose or hirsute at the lowermost sheath, especially distally; ligules shorter than 1 mm; blades 8-35 cm long, 5-15 mm wide, ascending or spreading, abaxial surfaces glabrous, adaxial surfaces usually scabridulous or pubescent, bases slightly narrowed, margins scabrous, apices long-tapering. Panicles 10-30 cm long, less than 1 cm wide; branches mostly short, appressed-ascending, with fascicles of congested spikelets; ultimate branchlets 1-sided; pedicels 0.2-1.8 mm. Spikelets 2-2.8 mm, subsessile, lanceoloid, slightly laterally compressed, glabrous, acute. Lower glumes about 1/2 as long as the spikelets, slightly keeled along the midveins, 3-veined, acute; upper glumes and lower lemmas similar, glumes slightly shorter than the lemmas, faintly keeled on the back, acute; lower florets staminate; lower paleas subequal to the lower lemmas; upper florets 2-2.5 mm, 2/5 to almost as long as the spikelets, narrowly ellipsoid; upper lemmas relatively thin, flexible, pale, acuminate, clasping the paleas only at the base. 2n = 36, 40.

Panicum hemitomon forms extensive, nearly pure stands in water or wetsoils such as marshes, swamps, and along the shores of streams, canals, ditches, lakes, and ponds. It is restricted to the United States.

Panicum gymnocarpon: See Phanopyrum gymnocarpon

Panicum sect. Monticola Stapf

Plants annual or perennial. Culms usually weak, decumbent. Ligules membranous and ciliate, or lacerate. Panicles usually diffuse, sometimes contracted. Spikelets ellipsoid to obovoid, glabrous or pilose, veins evident. Lower glumes 1/3-1/2 as long as the spikelets, 0-3-veined; upper glumes and lower lemmas 3-5-veined; lower florets sterile; lower paleas small or absent; upper florets rugose, with bicellular microhairs. x = 9.

Three species of Panicum sect. Monticola grow in the Western Hemisphere. Two species grow in the Flora region, one of which is native to Asia.

31.   Panicum trichoides Sw.
Small-Flowered Panicgrass

Plants annual. Culms 15-100 cm tall, 0.5-1(2) mm thick, sprawling to erect, without cormlike bases, freely branching and rooting from the lower nodes; nodes prominent, glabrous or pubescent; internodes not succulent, pilose. Sheaths shorter than the internodes, rounded, hairs papillose-based; collars pilose; ligules 0.2-0.5 mm; blades 2-7 cm long, 5-20 mm wide, 4-6 times longer than wide, lanceolate, thin, flat, sparsely to densely pilose, hairs papillose-based, bases asymmetrically cordate to subcordate, lower margins ciliate, papillose. Panicles 4-24 cm, almost as wide as long, diffuse, partially included or exserted; primary branches to 10 cm, alternate, ascending to reflexed, branching in the distal 2/3; pedicels 9-20 mm, threadlike. Spikelets 1-1.4 mm long, 0.5-0.6 mm wide, not secund, lanceoloid to narrowly ovoid, plano-convex in side view, sparsely pubescent. Lower glumes 0.4-0.8 mm, 1/3-1/2 as long as the spikelets, 1-3-veined, subacute; upper glumes 0.8-1.2 mm, arising 0.2 mm above the lower glumes, 3-5-veined; lower florets sterile; lower lemmas 0.1-0.2 mm longer than the upper glumes, 3-5-veined; lower paleas 0.5-0.8 mm, hyaline; upper florets 0.8-1.2 mm long, 0.4-0.6 mm wide, finely rugose, lemmas strongly convex. 2n = 18.

Panicum trichoides grows in moist, often weedy fields, woodlands, and savannahs of Mexico, Central and tropical America, and the Caribbean. It has been found, as a weed, in Brownsville and Austin, Texas, and is probably introduced to the Flora region. It has also been introduced into Africa, tropical Asia, and the Pacific islands. In the Flora region, it flowers from August through October

32.   Panicum bisulcatum Thunb.

Plants annual; loosely tufted, sprawling. Culms 30-150 cm tall, 2-4 mm thick, erect or spreading from a geniculate, non-cormous base, not succulent, glabrous throughout. Sheaths shorter or longer than the internodes, rounded, often with minute purple streaks, glabrous, margins shortly ciliate; ligules to 0.8 mm; blades 5-28 cm long, 4-14 mm wide, linear, more than 10 times longer than wide, thin, flat, glabrous on both surfaces or sparingly pilose adaxially, bases scabridulous near the margins, prominently veined. Panicles 12-30 cm long, 9-20 cm wide, usually 1-1.3 times longer than wide, diffuse; primary branches 8-15 cm, alternate, divergent, slender, scabridulous, much branched, branches confined to the distal 2/3, secondary branches spreading, spikelets confined to the distal 1/2 of the branches; pedicels 0.5-6 mm. Spikelets 1.8-2.7 mm long, 0.8-1 mm wide, ellipsoid, dark green, often purple-tinged, usually glabrous, acute to acuminate. Lower glumes 1/3-1/2 as long as the spikelets, glabrous, deltoid, acute; upper glumes and lower lemmas subequal, equaling or exceeding the upper florets, smooth, faintly 5-veined, sparsely pilose with short hairs near the margins and apices, acute; lower florets sterile; lower paleas absent or much shorter than the lower lemmas; upper florets 1.5-1.8 mm, ellipsoid, smooth, lustrous, grayish-brown at maturity, apices sparsely puberulent, obtuse to subacute. 2n = 36.

Panicum bisulcatum is an Asian species that grows in wet, open areas. It has been introduced sporadically, but has rarely become established, on the coastal plain of Georgia and South Carolina. The records from Philadelphia, Pennsylvania are from 1865-1877.

Panicum sect. Verrucosa (Nash) C.C. Hsu

Plants annual. Culms weak, sprawling. Ligules membranous, ciliate, very short. Panicles open, diffuse, lax, with a few spikelets. Spikelets warty-tuberculate or verrucose, faintly veined. Lower glumes less than 1/5 as long as the spikelets, without veins; upper glumes and lower lemmas subequal, 5-veined; lower florets sterile; lower paleas absent; upper florets finely longitudinally rugose, papillose and with bicellular microhairs, often with a minute protuberance at the base of the paleas. x = 9.

33.   Panicum verrucosum Muhl.
Warty Panicgrass

Plants annual; weak, ascending or sprawling. Culms 10-150 cm, slender, wiry, erect at first, ultimately decumbent, sprawling, glabrous, often with purple dots and streaks, branching extensively at the base, rooting at the lower nodes. Sheaths often shorter than the internodes, loose, glabrous, margins short-ciliate; ligules 0.2-0.5 mm, membranous, erose, ciliate; blades 5-20 cm long, 3-10 mm wide, thin, flat, glabrous on both surfaces, margins scabridulous, apices long-acuminate. Panicles 5-30 cm, nearly as wide as long; branches few, capillary, with a few spikelets distally; pedicels 0.5-10 mm. Spikelets 1.7-2.2 mm long, about 1 mm wide, ellipsoid or obovoid, glabrous, faintly veined, subacute or obtuse at the apices. Lower glumes 0.3-0.8 mm, reduced, acute; upper glumes and lower lemmas subequal or the glumes shorter, distinctly verrucose, with hemispheric warts; upper florets 1.6-2 mm long, about 1 mm wide, grayish-brown, dull, minutely papillose, acute. 2n = 36.

Panicum verrucosum grows primarily in open, moist or wet sandy areas bordering swamps, marshes, or lakes or on roadside ditches; it also grows occasionally in open, drier woodlands. It is restricted to the eastern United States and is mostly, but not exclusively, coastal.

34.   Panicum brachyanthum Steud.
Prairie Panicgrass

Plants annual; weak, ascending or spreading. Culms slender, wiry, glabrous, often with minute purple streaks and dots, ascending from a decumbent base, often branching extensively at the base and rooting at the lower nodes. Sheaths usually shorter than the internodes, glabrous, margins short-ciliate; ligules usually less than 0.3 mm, membranous, erose, ciliate; blades 4-15 cm long (rarely longer), 2-3 mm wide, flat or slightly involute, glabrous on both surfaces, margins scabridulous, especially towards the apices, bases narrowed. Panicles 4-17 cm, 1/2 to nearly as wide as long; branches few, capillary, ascending or spreading, scabridulous, with a few spikelets distally; pedicels 0.5-10 mm. Spikelets 3.2-4 mm long, about 1.5 mm wide, broadly ellipsoid or obovoid, tuberculate, hispid, faintly veined, acute or acuminate at the apices. Lower glumes usually less than 1 mm, obtuse or acute; upper glumes and lower lemmas subequal, distinctly tuberculate, hispid, with stiff hairs arising from wartlike bases; upper florets 2.7-3.2 mm long, 1.3-1.6 mm wide, obovoid or ellipsoid, nearly smooth, minutely papillose, or cross-rugulose, subacute to acute. 2n = unknown.

Panicum brachyanthum grows in dry, sandy or clayey soils of open areas, remnant prairies, woodland borders, and roadsides and, less commonly, along the margins of bogs and on grassy shores in the western portion of the gulf coast plain. It is restricted to the southern United States. It resembles P. verrucosum in its growth habit, but is more restricted in its distribution.