Hygrophila polysperma (Roxb.) T. Anderson
Miramar weed, Indian swampweed, East Indian hygrophila
Fruit a capsule with 20–30 seeds. Seeds compressed, obovate or elliptic to round, 0.4–0.62 mm long, 0.3–0.5 mm wide, 0.02–0.06 mm thick. Entire margin winged; wing narrow or barely apparent. Testa minutely pebbled, glistening, orange-yellow to brownish-yellow, translucent where seed particularly thin. Hilum marginal, a raised narrowly elliptic rim. Embryo spatulate.
native to the Indian subcontinent, Indochina, and Malaysia
introduced to the United States
deep water and along the banks; prefers flowing streams, but also grows in slow-moving waters and lakes; marshes, canals, rivers, swamps, irrigation ditches
Hygrophila polysperma is a mostly submersed freshwater perennial herb, usually attached, up to 3 m long. It was introduced to the U.S. as an ornamental plant in the aquarium trade. However, it has become naturalized, forming dense stands and floating mats, which obstruct water flow and navigation. The plant is more herbicide tolerant and less appetizing to the grass carp than Hydrilla verticillata. As a consequence, it has replaced Hydrilla as the major aquatic weed in parts of Florida. Hygrophila polysperma reproduces vegetatively by whole plants, plant fragments and rooting at the nodes.