Fanwort (Cabomba caroliniana)

Description

Fanwort is a freshwater, submersed, perennial plant with short, fragile rhizomes. It is usually rooted in the substrate, but sometimes found drifting. Its stems are green to reddish brown. It has two types of leaves: submersed and floating. The submersed leaves are arranged in pairs or in whorls along the stem and the floating leaves are diamond shaped and are arranged in an alternating pattern. It has small white, pink or purple flowers that float on the surface and grow from the tips of the stems.

Look-alikes

Fanwort is often confused with watermilfoils (Myriophyllum), water buttercup (Ranunculus aquatilis) and Beck's watermarigold (Megalodonta beckii). The leaves of watermilfoils are whorled and the plants have small, flowers growing from where its leaves meet the stem. Water buttercup has alternately arranged leaves. Beck’s watermarigold has yellow, composite flowers and sessile leaves, while Fanwort has white flowers and slender leaves.

Impacts & Habitat

Fanwort is native to the subtropic-temperate regions of southeastern U.S. It currently grows from Texas to Florida, north to Massachusetts and west to Kansas, including several counties in Michigan and New York. Fanwort prefers lakes and ponds, but can also be found in slow-moving rivers, streams, sloughs and ditches. Fanwort primarily reproduces via regrowth of stem or rhizome fragments, but can reproduce via seed. A small fragment can regenerate a whole plant that in turn, can reproduce clonally and spread rapidly, often replacing native species. It flowers from May to September, yet viable shoots have been observed in January beneath ice. Fanwort can form dense stands that clog drainage systems and interfere with swimming and boating. Plant fragments can be transported in rivers, streams or floodwaters, and by adhering to migrating wildlife and boats.

Control

Fanwort appears to be less sensitive to herbicides than other aquatic plants and appears to get most of its nutrients from the water column. Therefore, it may be sensitive to reduction of nutrients in the water. The herbicides endothall and fluridone provide excellent control. In some cases, water level draw downs have been used to reduce fanwort growth by drying the plant and seeds. Grass carp will eat fanwort, but it is not a preferred food. However, carp are non-native to Wisconsin and are usually a nuisance species. After visiting a water body, it is prudent to inspect boats and equipment for plant fragments so as to prevent further spread.

Additional Information (Links exit DNR)

USDA
USGS
Fanwort - A Problem Aquatic Plant in Washington
Center for Aquatic & Invasive Plants
University of Massachusetts Amherst