Panicum amarum S. Elliott var. amarum and P. amarum var. amarulum (A.S. Hitchcock & M.A. Chase) P. Palmer are New World tropical-, subtropical-, and temperate-zone rhizomatous varieties of a grass species that is important on coastal foredunes and primary dune topographic facets. Herein, we present a review of the biology of these important taxa. Panicum amarum has low freshwater moisture requirements, and it tolerates low nutrient levels, high sand temperature, and extensive sand coverage. Also known as bitter panic grass, it inhabits mobile and semistable dune systems, and it plays a significant role in trapping sand and building primary dunes. Panicum amarum quickly recolonizes coastlines where all vegetation has been removed by storm surges.