Common Names: European waterstarwort

Description: Difficult to distinguish from other Callitriche species unless fruit is present; survey in late summer and fall. It can be distinguished by its fruits, which are almost round (orbicular).

Habit: Aquatic; perennial, delicate.

Leaves: Tiny, opposite, entire, forms vary, floating leaves spatulate, submergent leaves linear.

Stems: 10-30 cm (4-12 in) in length, usually branched, rising to surface or sprawling.

Flowers: Tiny flowers lack sepals and petals and are located at the leaf bases on minute stalks, 2-4 tiny whitish bracts emerge from the flower base.

Fruit and seeds: Small, located at the leaf bases. Four compartments, each containing one seed. Pond: Oval, 1.2-1.8 mm long, 1.2-1.7 mm wide, narrow margin all around (wing); bracts at base. Autumnal: 1.1 to 1.6 mm long, 1.2 to 1.8 mm wide, no margin, fruit without bracts.

Habitat: Native to Europe. Found in shallow waters of pond, marches or in protected areas in lakes or streams with slow-moving water.

Reproduction: By seed and clonally, dispersed by boats, vehicles, and animals-the latter both by fragments and ingested seed. Not all produce seeds.

Similar species: Hard to distinguish from other water-starworts (Callitriche spp.) when not in fruit.

Monitoring and rapid response: Hand-pulling, cutting or raking making sure to remove all fragments. Clearing off boats and other water-related equipment will help prevent spreading.

Credits: The Michigan Natural Features Inventory (MNFI) has partnered with MISIN to provide the information in this fact sheet. Species images and/or information were used with permission from "A Field Identification Guide to Invasive Plants in Michigan's Natural Communities" and "A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan.

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