Indian swampweed (Hygrophila polysperma)

Common Names: Miramar weed, East Indian hygrophila

Description: This species is listed on the Federal Noxious Weed list. Square stems may aid in identification.

Habit: Herbaceous perennial, rooted, dicot, primarily aquatic. Rare terrestrial form in moist soils.

Leaves: Opposite, sparsely hairy, elliptic to oblong, up to 6 cm (1.5 in) long and 2 cm (0.5 in) wide, variable colors; light green to brown to reddish.

Stems: Creeping ascendant (rarely erect); up to 6ft in length or longer; upper most emersed stems may be squarish; brittle and easily break into fragments.

Flowers: Small, 3/8 in long; solitary; no stalks; found in leaf axils in the upper parts of the immersed stems; bluish-white to white petals; hairy; two "lips", upper lip 2-lobed, lower lip 3-lobed; calyx is hairy with 5 equal lobes; blooms October through March.

Fruit and seeds: Narrow capsule 6-7 mm long; 20-30 tiny flattened-round seeds.

Habitat: Native to India. Found in lakes, streams and rivers, still and moving water, up to 3 m (10 ft) in depth. Grows from bottom to water surface.

Reproduction: Vegetatively, by small stem and leaf fragments, possibly by seed; spread by mechanical harvesters, boats and water currents.

Similar species: Alligatorweed (Alternanthera philoxeroides) has large, white, papery flowers.

Monitoring and rapid response: Difficult to control, only herbicide known to work contains the ingredient, endothall.

Credits: The information provided in this factsheet was gathered from the Michigan Natural Features Inventory and the University of Florida Institute of Food and Agricultural Sciences.

Individual species images that appear with a number in a black box are courtesy of the Bugwood.org network (http://www.invasive.org).Individual photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (http://images.google.com).

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