Fanwort leaves and flower

Fanwort (Cabomba caroliniana)

Fanwort is a perennial submersed or sometimes floating aquatic herb. Fanwort native to the southeastern United States, but is easily spread and has created nuisance conditions as far north as New York, Michigan, and Oregon.

Overview

Regulated areas of Fanwort
Fanwort is Prohibited (Red counties)

Other names for this plant include:

  • Common names: Carolina fanwort, fish grass, Carolina water-shield
  • Scientific names: Cabomba caroliniana var caroliniana; C. australis

Ecological threat:

  • Forms dense stands in some areas, crowding out other vegetation, clogging streams and drainage canals, and interfering with recreational, agricultural, and aesthetic water uses.
  • Control is difficult, as fragmentation can cause resprouting.

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for fanwort was based upon this literature review developed by the department.

Identification

Leaves: Tightly spaced; submersed leaves have petioles and a tubular appearance, are finely divided, less than 1” long and 2” wide, fan-shaped and arranged in pairs on the stem or whorled; floating leaves (when present) are 0.25-0.75” long, inconspicuous, diamond-shaped with stem attached in the center, and alternate on stems.

Flowers: White with yellow centers; less than 0.5” in diameter; at the end of 1-4” long peduncles; floating; bloom May to September.

Roots: Short rhizomes with fibrous roots.

Similar species: Fanwort looks similar to coon's-tail (Ceratophyllum spp.), milfoils (Myriophyllum spp.), water buttercup (Ranunculus aquatilis), and Beck's watermarigold (Megalodonta beckii). The leaves of milfoil species are whorled and the plants have small, asillary flowers. Water buttercup has alternate leaves and Beck's marigold has yellow composite flowers and sessile leaves.

Distribution

Currently, there have not been reports of fanwort in WI. Have you seen it? Send us a report.

Control

Mechanical: Water-level drawdowns have reduced growth in some areas in the South, but extreme drying is necessary to prevent regrowth from seed. A venture dredge (like a giant vacuum cleaner) can overcome the problem of fragmentation, and reduce populations.

Chemical: Endothall and floridone may be effective herbicide treatments.

Photos

View fanwort pictures in our photo gallery!

Resources

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Last revised: Wednesday December 19 2012