European frog-bit leaves and flower

European frog-bit (Hydrocharis morsus-ranae)

A free-floating annual aquatic herb in the Frog’s Bit family. Can dramatically affect native aquatic life and limit recreational activities.

Overview

Regulated areas of European frog-bit
European frog-bit is Prohibited (Red counties)

Other names for this plant include:

  • Common names: common frogbit

Ecological threat:

  • Invades shallow, quiet, or slow-moving water; edges of lakes, rivers, and streams; swamps, marshes, and ditches.
  • Forms large colonies of dense, floating mats that can dramatically affect native aquatic life and limit recreational activities.

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 European frog-bit was based upon this literature review developed by the department.

Identification

Leaves: Usually floating; resemble tiny water lilies; kidney-shaped with long stems; 0.5-2.25” in diameter; smooth; often dark purple beneath; lateral veins are arching and make a 75-90 degree angle with the midvein; tissue containing airpockets are located mostly along the midvein. Lower leaf surfaces are dark purple in color.

Flowers: White; cup-shaped; three petals with yellow dots at base; bloom mid-summer.

Fruits & seeds: Rarely produces seeds and instead relies on vegetative reproduction.

Roots: Long, cord-like stolons form large floating mats of connected plants. It also forms turions.

Similar species: Often confused with American frog-bit (Limnobium spongia), a species whose leaves have lateral veins that make a 30-80 degree angle with the midvein, and whose leaf tissue contains large air pockets throughout.

Distribution

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

Control

Mechanical: Other than hand-pulling, there are no known control methods.

Photos

View European frog-bit pictures in our photo gallery!

Resources

Sources for content:

  • Czarapata, Elizabeth; Invasive Plants of the Upper Midwest: an illustrated guide to their identification and control. University of Wisconsin Press. 2005. Pg. 146
  • Global Invasive Species Database: European frogbit [exit DNR].
  • Invasive Plant Atlas of New England: European frogbit [exit DNR]

Links for More Information

Last revised: Wednesday December 19 2012