Hygrophila polysperma

Name and classification

Hygrophila polysperma (Roxb.) T. Anderson
Family Acanthaceae

Common names

Miramar weed, Indian swampweed, East Indian hygrophila

Disseminule

seed

Description

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.

Distribution

native to the Indian subcontinent, Indochina, and Malaysia

introduced to the United States

Habitat

deep water and along the banks; prefers flowing streams, but also grows in slow-moving waters and lakes; marshes, canals, rivers, swamps, irrigation ditches

General information

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.

seeds

seeds

hilum of seed

hilum of seed

A, seed; B, longitudinal section of seed showing embryo in situ; C, transection of seed; drawing by Lynda E. Chandler

A, seed; B, longitudinal section of seed showing embryo in situ; C, transection of seed; drawing by Lynda E. Chandler

dehisced fruit (seeds released)

dehisced fruit (seeds released)