Waterthyme Hydrilla verticillata

Waterthyme is an invasive rooted aquatic plant in the Hydrocharitaceae family and is native to  Asia, Africa and Australia. It is the only species in the genus but many consider it to have several variations. It was introduced through the aquarium trade and was subsequently dumped into the waterways. It can now be found from Connecticut south to Florida, into the central USA, west to Texas and up the Pacific coast. It is found throughout NC in various freshwater systems.

It is considered one of the worse invasive plants in this country and the world and is on the USDA Noxious Weed List. It is listed as invasive by the NC Invasive Plant Council and many other states.

The stems are slender and branched, up to 25’ long. The leaves are in bottle-brush whorls of 3-8 with serrated margins, reddish midribs and undersides with small sharp teeth. Tiny white flowers have 6 petals and grow on long stalks. There are both monoecious (both male and female flowers on the same plant) and dioecious (male and female flowers on different plants) forms. The plants are spread both by seeds and vegetatively. They overwinter in colder climates by their tubers.

In addition to forming large monoculture mats that crowd out native plants and alter the ecosystem, the plant harbors bacteria that cause a brain-wasting disease in waterfowl. It is very versatile and can grow in almost any freshwater system including springs, lakes, marshes, ditches, rivers and tidal zones in water a few inches and up to 20 feet deep. It can grow sun to shade

Insects, Diseases, and Other Plant Problems: No significant problems. Invasive in many states including NC. See native alternatives to the left.