Federal Noxious Weed List

Hygrophila polysperma

East Indian hygrophila

Introduction

Origin: India, Malaysia
Introduction to Florida: 1950s (ornamental)

East Indian hygrophila is mostly submersed, with a few inches sometimes emersed above the water. East Indian hygrophila is not a native plant. It may be found in streams and in slowly moving waters.

 

Description

Hygrophila stems are square. The submersed stems grow to six feet long. Its leaves are opposite on the stem. Leaves are 1 1/2 inch long and 1/2 inch wide. East Indian hygrophila flowers are bluish-white to white, and have two lips. They grow from the axils where the leaves meet the stems.

Habit

  • herbaceous perennial
  • amphibious, “obligate” (requiring a wet habitat)
  • in freshwaters, mostly submersed, partly emersed
  • growing from bottom to surface in water to 10 feet deep, or found creeping along edges
  • forming dense stands of stems in the water, later in the season breaking loose to form large floating mats
  • rarely, terrestrial growth form grows in moist soil (McCann)
  • flowering in fall and winter
  • reproduces asexually (regrows from plant fragments) and perhaps sexually (from seed), however Sutton (1996) says it’s unknown whether seeds play a major part in its spread
  • stems fragment easily and are able to develop new plants from small fragments; reportedly even a free-floating leaf can form a new plant

Habitat

  • in warmer climates; preferring flowing streams, but also may be found in slow-moving waters and in lakes
  • temperature tolerance: minimum temperature, 4o C (39o F); optimum temperature, 22-28o C (71-82o F); maximum temperature, 30o C (86o F) (Kasselmann 1995)
  • best light intensity for hygrophila growth is around 110 micro-einsteins/meter squared/hour (Cobb and Haller, 1981) (what is light intensity of site under trees in warm weather?)
  • low light compensation and saturation points and low CO2 compensation point make it a competitive plant because it can start growing in low light before other plants do (Spencer & Bowes 1985, Bots et al. 1990 – from Angerstein 1994)
  • tolerates a range of pH and water hardness conditions

Hygrophila polysperma (Roxb.) T. Anderson
Original description: J. Linn. Soc., Bot. 9:426. 1876.

  • dicot
  • rooted in the hydro-soil
  • stems creeping ascendant (rarely erect); to 6 feet and longer; upper most emersed stems may be squarish; stems are brittle and easily break into fragments
  • leaves opposite (on the stem); simple; sparsely hairy; with pointed tips (acute)
  • leaf color variable, light green to brown to reddish
  • leaves submersed and emersed are more or less the same shape; mostly 1.5 in. long, .5 in. wide, but can be larger
    • emersed leaves elliptic to obovate-elliptic; having no leaf stalks (sessile)
    • submersed leaves larger and thinner than emersed leaves, broadly elliptic, broader toward tip; having short stalks
  • flowering in fall and winter (in Florida), October to early March (Sutton 1996)
  • flowers small, to 3/8 in. long, solitary, without stalks; found in leaf axils (angle where leaf meets the stem) in the apical (uppermost) parts of the emersed stems; corolla (petals) bluish-white to white, hairy, with two “lips”, upper lip 2-lobed, lower lip 3-lobed; calyx (leaves covering the bottom part of the flower) hairy with 5 equal lobes
  • rooting at stem nodes; many roots
  • fruit a narrow capsule 6-7 mm long; 20-30 tiny flattened-round seeds

Hygrophila polysperma with small, opposite-leaves, may sometimes be confused with submersed or partially submersed plants such as:

Non-native alligator weed (Alternanthera philoxeroides): alligator weed has largish white papery flowers which are totally different native red ludwigia (Ludwigia repens): red ludwigia has yellow flowers with 4 petals (however the petals fall off quickly, so they are rarely seen); purple pigment throughout, especially in submersed leaves; blunt leaf tips native lake hygrophila (Hygrophila costata (H. lacustris)): lake hygrophila is entirely emersed or terrestrial; much larger and taller (to 80 cm); mostly erect; much larger leaves; flowers along the entire stem (rather than just at the top).

Impacts
  • Hygrophila polysperma is a fast-growing and fast-spreading invasive that can outshade and therefore outcompete other submersed plants; it can occupy the entire water column; many adventitious roots at stem nodes means that fragments can easily grow.
  • Hygrophila polysperma clogs irrigation and flood-control canals; in south Florida, large mats of fragments collect at culverts and interfere with essential water control pumping stations; it interferes with navigation; and it’s even able to compete with another aggressive non-native invasive plant, hydrilla, and is replacing hydrilla in some Florida locations.
  • Hygrophila reportedly grew on Lake Tohopekaliga (Florida) from 0.1 acre in 1979 to 10 acres in 1980 (MITRE).

Management Plan


Preventative

First, clean your boat before you leave the ramp! Transporting plant fragments on boats, trailers, and in livewells is the main introduction route to new lakes and rivers.

But, there’s plenty more you can do to help.

Cultural Mechanical

the action of mechanical harvestors and chopping machines fragment the hygrophila plants and increase their distribution

Biological

the herbivorous (plant-eating) biological control fish, the Chinese grass carp, have a low preference for hygrophila (Cassani); triploid grass carp reportedly were “used successfully in canals to control hygrophila” (Ferriter et al. in Simberloff 1997, p. 319); no other biological control work has been done for this species (Pemberton, 1996).

Chemical

registered aquatic herbicides provide only marginal control of hygrophila; hygrophila is relatively resistant to herbicides that control hydrilla (Vanadiver 1980; Sutton 1996); hygrophila is much more difficult to control with herbicides than is hydrilla, and requires higher rates of herbicides (Hall and Vandiver, 1990); treatments using copper plus Reward herbicides combined showed little effect on this plant in Florida canals 4 weeks after application (Sutton 1996)

From the University of Florida Aquatic Weed Management Guide, Vandiver 1999:

  • According to this Guide, the only herbicide labelled to be used against hygrophila is “Aquathol Super K Granular Aquatic Herbicide”, having the active ingredient, “endothall”. This herbicide is labelled to be legally used in Florida canals, drainage ditches, lakes, ponds, reservoirs, rivers and streams. It is unknown at this time to this author whether this herbicide may legally be used against hygrophila in other states. As always, comply with federal law by following the herbicide label instructions, permissible sites and application rates.