Panicum amarum subsp. amarulum
Plants with short (usually) or ascending rhizomes. Culms usually 100-250 cm, robust, decumbent, densely bunched (occasionally with more elongated rhizomes and less bunching in the southern part of its range). Panicles usually more than 5 cm wide, spikelet density high; primary branches usually 2 or more per node, smooth to moderately scabrous, usually with quaternary branching. Spikelets 4-5.9 mm; lower glumes 3-5-veined, veins less evident than in subsp. amarum, midvein smooth distally.
Discussion
Panicum amarum subsp. amarulum grows in swales behind the first dune and on sandy borders of wet areas. It extends as far north as northern New Jersey and extends southward into Mexico. It has been introduced to Massachusetts, West Virginia, Cuba, and the Bahamas.
Panicum amarum subsp. amarulum is a fertile tetraploid, and possibly a progenitor of subsp. amarum, with which it intergrades in the Gulf region. Plants that intergrade with P. virgatum are evident in some coastal areas; they may represent hybrids.
Selected References
None.