Pond water-starwort
(Callitriche stagnalis)
Small, delicate plants usually found in shallow water and loosely rooted to the bottom. It is an aquarium plant and could be introduced into natural areas through the dumping of aquarium vegetation and spread by birds.
Overview
Other names for this plant- Common names: common starwort, common water-starwort, water chickweed
- Found in shallow waters and may threaten biological diversity by shading and crowding out other species.
Classification in Wisconsin: Caution. This is a non-regulated category.
Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for pond water-starwort was based upon this literature review [PDF] developed by the department.
Identification
Leaves: Opposite, narrow and submersed (up to 10 mm wide) with one rounded leaf tip are sometimes present; oval or spoon-shaped floating leaves are up to 10 mm wide joined by tiny ridges at the base.
Flowers: Tiny, lack sepals and petals and located at the leaf bases on minute stalks with two to four tiny whitish bracts emerge from the flower base.
Fruits & seeds: Small, located at the leaf bases; four compartments, each containing one seed; oval, 1.2-1.8 millimeter long, 1.2-1.7 millimeter wide, narrow margin all around (wing); bracts at base.
Roots: Fibrous, from plant base or sprouting from stem joints.
Similar species: May be confused with other starworts. To be sure of the identification, the surfaces of mature fruit need to be examined under 10-20x magnification.
Control
Mechanical: Dredging can deepen a waterbody to a depth where pond water-starwort cannot receive enough light for growth. However, dredging is expensive, particularly if the sediments of a waterbody are contaminated, and require disposal. Cutting pond-water starwort can be viable, but the plant fragments must be removed to prevent regrowth. Shading has been successful at impeding growth; however, shading an entire waterbody or large areas of a waterbody would be difficult and expensive.
Resources
Sources for content- Washington State Department of Ecology. Aquatic Plants: Callitriche stagnalis Scop., pond water-starwort [exit DNR].
- Midwest Invasive Plant Network: Pond Water Starwort Factsheet [exit DNR]
