Hygrophila is a perennial plant that forms dense colonies and can grow to the surface in water to a depth of 10 feet. Hygrophila is highly branched. Hygrophila can grow from seeds and from stem fragments. Stems fragment easily. One distinguishing characteristic of hygrophila is its squarish stems. Leaves are opposite and blade-like up to 3 inches long and 4/5 inch long with smooth margins. The leaves are usually wider near the tip and are joined at the node (i.e. site of attachment to the stem) by projections coated with cilia (i.e. fine hair-like structures). New roots can form at the nodes of the leaves. Flowers are small, singular, bluish white in color and found only in the upper leaf axils. The flowers are virtually concealed by the leaves.
Hygrophila is native to India and Malaysia and was probably brought to the U.S. for the aquarium industry. It is considered a noxious pest because it grows so rapidly, out competing and eliminating native species.
Hygrophila can be confused with the native water primrose (submerged type) but water primrose does not have the fingerlike projections at the base of the leaves nor the squarish stem. Hygrophila can be completely submerged or stand above the water like an emergent plant.
Submerged portions of all aquatic plants provide habitats for many micro and macro invertebrates. These invertebrates in turn are used as food by fish and other wildlife species (e.g. amphibians, reptiles, ducks, etc.). After aquatic plants die, their decomposition by bacteria and fungi provides food (called “detritus”) for many aquatic invertebrates.
Hygrophila is not native to North America and is on the Federal Noxious Weed List.