Panicum virgatum
Panicum bergii
panic raide, switch grass, switch panicgrass
Berg's panicgrass, Bergs witchgrass
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.
(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.
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.
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.
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.
(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.
2.5-8 mm long, 1.2-2.5 mm wide, narrowly lanceoloid, turgid to slightly laterally compressed, glabrous, acuminate.
2-3 mm long, 0.8-1.2 mm wide, 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 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.
= 18, 21, 25, 30, 32, 35, 36, 54-60, 67-72, 74, 77, 90, 108.
= 36.
Panicum virgatum
Panicum bergii
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 bergii is an eastern South American species that now grows in southeastern Texas. It occurs in ditches and shallow, and sporadically flooded depressions in grasslands.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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