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Callitriche palustris and Callitriche heterophylla


common water starwort in-situ
Common water starwort in-situ

Habitat:Maine is home to two water starwort species: common water starwort (Callitriche palustris) and large water starwort (Callitriche heterophylla). Both are found in the submersed and floating leaf plant communities. Water starworts are generally found in quiet, cool (often spring-fed) waters or along muddy shores, preferring muddy or sandy substrates.

Description:Maines two water starwort species share many common characteristics. Both water starworts have fine stems that are 10 to 20 cm long. The submersed leaves are opposite, and arranged in pairs or in groups of three. The delicate leaves are simple, entire and variable in appearance. The submersed leaves tend to be pale green and linear. The upper leaves are more rounded (5mm wide) and crowded at the tip, forming a rosette that floats on the surface. The flowers grow in the axils of the leaves and produce very small capsule-like fruits (1 to 1.4 mm).

The fruits provide the best means of distinguishing between the two species. The fruits of common water starwort are 2mm longer than they are wide, winged, with a shallow groove between the wings, and surface pits arranged in vertical rows. The fruits of large water starwort are nearly as wide as they are long (no more than 1 mm longer than wide), sometimes with shallow grooves, but no wings. The surface has pit-like markings, but they are not in rows.

large water starwort Range Map
U.S. range map of large water starwort

common water starwort Range Map
U.S. range map of common water starwort

U.S. Range:Both water starworts are native to Maine, New England and much of the United States.

Annual Cycle:Water starworts are annuals that reproduce by seed and stem fragments. Because the plants are adapted to cool water, growth begins early and flowers bloom in early summer. Seeds are mature by mid to late summer.

Value in the Aquatic Community: The stems and fruits of starworts are grazed by duck and other waterfowl. The branching stems offer shelter and foraging opportunities for fish.

Look Alikes: May be confused with hydrilla, Brazilian elodea, and mare's tail.

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common and large water starwort common water starwort in-situ large water starwort range map common water starwort range map large water starwort flower large water starwort fruit large water starwort habit common water starwort flower common water starwort fruit common water starwort habit common water starwort habit

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