West Indies, tropical Central and South America
Possibly a natural introduction by migratory birds; can form extensive colonies in its natural habitats.
Robust perennial grass from stolons. Stems floating, creeping, or ascending to 1 m (3 ft) or more in height, sparingly branched, rooting at the lower nodes; stems pithy, not hollow. Leaf sheaths glabrous but with hairs on upper margins; ligule a membrane. Leaf blades flat, to 35 cm (14 in) long and to 4 cm (1.6 in) wide, cordate at the base and clasping the stem (amplexicaul); glabrous but with long hairs on lower margins. Inflorescence a terminal panicle, dense and spike-like, about 8 mm (0.3 in) wide and to 50 cm (20 in) long; spikelets short stalked, 3.3-4.3 mm long, scabrous on the veins, often opened slightly at the apex.
May be confused with the native Sacciolepis striata (L.) Nash, American cupscale, which has a similar inflorescence, or with other marsh grasses of similar form, but Hymenachne stems distinctive in containing white pith (most grass stems are hollow)
Adapted to fluctuating water levels, i.e., cycles of flooding and drying, which allow massive regeneration by seed and ensure persistence after extensive drought periods (Wildin 1988). Observed as tolerating 40 weeks of flooding and maximum flooding depths of 1.2 m (4 ft) (Tejos 1980). Flowers in the fall (Wunderlin 1982), with observed germination rates variable, 0-86% (Hill 1996). Seed more widely dispersed during periods of high standing water.
Central and South Florida
The best approach to managing West Indian marsh grass in uninfested areas is to prevent its introduction. Once introduced, the appropriate method of control must be considered on a case-by-case basis, depending on the site conditions and level of infestation. Several control methods are available and an integrated pest management approach is recommended. Park rangers and the South Florida Water Management District have used registered systemic herbicides to control marsh grass by killing the buried stolon