Panicum virgatum
Panicum tenerum
panic raide, switch grass, switch panicgrass
blue-joint 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.
40-100 cm, erect, simple or branching from the lower nodes;
nodes glabrous;
internodes 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.
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.
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.
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.
2.5-8 mm long, 1.2-2.5 mm wide, narrowly lanceoloid, turgid to slightly laterally compressed, glabrous, acuminate.
1.8-2.8 mm long, 0.8-1 mm wide, usually subsessile, lanceoloid to narrowly ovoid, green, often purplish-stained, glabrous, acute.
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 0.9-3 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.
= 18, 21, 25, 30, 32, 35, 36, 54-60, 67-72, 74, 77, 90, 108.
= 20.
Panicum virgatum
Panicum tenerum
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 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 P. rigidulum, particularly P. rigidulum subsp. pubescens.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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