Panicum virgatum
Panicum hirsutum
panic raide, switch grass, switch panicgrass
giant witchgrass, hairy panicgrass
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.
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 with papillose-based hairs below the nodes.
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.
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.
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.
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.
2.5-8 mm long, 1.2-2.5 mm wide, narrowly lanceoloid, turgid to slightly laterally compressed, glabrous, acuminate.
1.8-2.5 mm long, 0.5-1 mm wide, narrowly ellipsoid, glabrous.
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.
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.
= 18, 21, 25, 30, 32, 35, 36, 54-60, 67-72, 74, 77, 90, 108.
= 36.
Panicum virgatum
Panicum hirsutum
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.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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