Panicum virgatum |
Poaceae subfam. panicoideae |
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panic raide, switch grass, switch panicgrass |
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Habit | Plants perennial; rhizomatous, rhizomes often loosely interwoven, hard, with closely overlapping scales, sometimes short or forming a knotty crown. | Plants annual or perennial; synoecious, monoecious, or dioecious; primarily herbaceous, habit varied. | ||||||||
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. |
annual, usually solid, sometimes somewhat woody, sometimes decumbent, often branched above the base. |
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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. |
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Leaves | distichous; sheaths usually open; auricles usually absent; abaxial ligules usually absent, occasionally present as a line of hairs; adaxial ligules membranous, sometimes also ciliate, or of hairs, sometimes absent; blades sometimes pseudopetiolate; mesophyll radiate or non-radiate; adaxial palisade layer absent; fusoid cells usually absent; arm cells usually absent; kranz anatomy absent or present; midribs usually simple, rarely complex; adaxial bulliform cells present; stomata with triangular or dome-shaped subsidiary cells; bicellular microhairs usually present, with a long, narrow distal cell; papillae absent or present. |
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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. |
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Inflorescences | ebracteate (Paniceae) or bracteate (most Andropogoneae) panicles, racemes, spikes, or complex arrangements of rames (in the Andropogoneae), usually bisexual, sometimes unisexual; disarticulation usually below the glumes, frequently in the secondary and higher order axes of the inflorescences. |
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Spikelets | 2.5-8 mm long, 1.2-2.5 mm wide, narrowly lanceoloid, turgid to slightly laterally compressed, glabrous, acuminate. |
bisexual or unisexual, frequently paired or in triplets, the members of each unit usually with pedicels of different lengths or 1 spikelet sessile. |
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Glumes | usually 2, equal or unequal, shorter or longer than the adjacent florets, sometimes exceeding the distal florets; florets 2(-4), usually dorsally compressed, sometimes terete or laterally compressed; lower florets sterile or staminate, frequently reduced to a lemma; upper florets usually bisexual; lemmas hyaline to coriaceous, lacking uncinate hairs, often terminally awned; awns single; paleas of bisexual florets well-developed, reduced, or absent; lodicules usually 2, sometimes absent, cuneate, free, fleshy, usually glabrous; anthers 1-3; ovaries usually glabrous; haustorial synergids absent; style branches 2, free and close or fused at the base. |
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Caryopses | hila usually punctate; endosperm hard, without lipid; starch grains simple; embryos large in relation to the caryopses, usually waisted; epiblasts usually absent; scutellar cleft present; mesocotyl internode elongated; embryonic leaf margins usually overlapping, rarely just meeting, x = 5, (7), 9, 10, (12), (14). |
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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. |
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2n | = 18, 21, 25, 30, 32, 35, 36, 54-60, 67-72, 74, 77, 90, 108. |
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Panicum virgatum |
Poaceae subfam. panicoideae |
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Distribution |
AL; AR; AZ; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; PA; RI; SC; SD; TN; TX; UT; VA; VT; WI; WV; WY; HI; MB; NS; ON; QC; SK
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Discussion | 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 taxa. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
The subfamily Panicoideae is most abundant in tropical and subtropical regions, particularly mesic portions of such regions, but several species grow in temperate regions of the world. Within the Flora region, the Panicoideae are represented by 59 genera and 364 species. They are most abundant in the eastern United States (Barkworth and Capels 2000). Photosynthesis may be either C3 or C4. All three pathways are found in the subfamily, but the PCK and NAD-ME variants appear to have evolved only once, while the NADP-ME pathways seems to have evolved several different times (Giussani et al. 2001). The Panicoideae were first recognized as a distinct unit by Brown (1814), earlier than any of the other subfamilial taxa of the Poaceae. Its early recognition is undoubtedly attributable to its distinctive spikelets. Recognition of the tribe Gynerieae is recent (Sanchez-Ken and Clark 2001) and its placement in the Panicoideae, rather than the Centothecoideae, should be regarded as tentative. Spikelets with two florets are found in many other subfamilies, but rarely do they follow the pattern of the lower floret being sterile or staminate and the upper floret bisexual. Development of unisexual florets within the Panicoideae appears to be consistent across the subfamily (LeRoux and Kellogg 1999), but differs from that in the Ehrhartoideae (Zaitcheck et al. 2000). The Paniceae and Andropogoneae have their conventional interpretation in this Flora, so far as the North American taxa are concerned. Molecular studies, however, while strongly supporting the monophyly of the Andropogoneae, show the Paniceae to be paraphyletic, with two distinct clades. In one of these clades, most taxa have a chromosome base number of x = 9, but some have x = 10, and the taxa are pan-tropical in origin. The taxa in the other clade, with one exception, have a chromosome base number of x = 10 and are American in origin. This latter clade is sister to the Andropogoneae, which also have a chromosome base number of x = 10 (Gomez-Martinez and Culham 2000; Giussanni et al. 2001; Barber et al. 2002). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 25, p. 474. | FNA vol. 25, p. 351. | ||||||||
Parent taxa | Poaceae > subfam. Panicoideae > tribe Paniceae > Panicum > subg. Panicum > sect. Repentia | Poaceae | ||||||||
Sibling taxa | ||||||||||
Synonyms | P. virgatum var. spissum, P. virgatum var. cubense, P. bavardii | |||||||||
Name authority | L. | Link | ||||||||
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