Flora of North America species comparison

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 is a large genus, but just how large is difficult to estimate because its limits are not yet clear. Many taxonomists would treat it as including Dichanthelium, Steincbisma, and some members of Urochloa. Recent work supports some aspects of the treatment presented here, but not all of them. For instance, Guissani et al. (2001) suggest that Panicum subg. Panicum is a monophyletic group that should have a rank equivalent to Dichanthelium and Steinchisma. The two other subgenera included here in Panicum, subg. Agrostoidea and subg. Phanopyrum, are not monophyletic, but the relationships of their species to other members of Panicum sensu lato are not well enough understood to suggest a better treatment, nor to justify the name changes a differing generic treatment would require.

Most species of Panicum are tropical, but many grow in warm, temperate regions. Of the thirty-four species occurring in the Flora region, twenty-five 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 serai 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, P. bulbosum, P. obtusum, 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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)