Callitriche stagnalis (pond water-starwort) and Callitriche hermaphroditica (autumnal water-starwort)


Species:	Callitriche stagnalis Scop., pond water-starwort Callitriche hermaphroditica L., autumnal water-starwort
Family:	Callitrichaceae
Water-starworts are small, delicate plants usually found in shallow water. All species in the Northwest are loosely rooted to the bottom with narrow underwater leaves and/or broadened floating leaves arranged in pairs along thin stems. Characteristics of water-starworts are quite variable and depend on growing conditions. To be sure of their identification to species, the surfaces of mature fruit need to be examined under 10-20x magnification. Pond water-starwort usually has spoon-shaped floating leaves crowded at the stem-tip, whereas autumnal water-starwort has only narrow, underwater leaves.

Leaf: Opposite. Pond: narrow submersed leaves (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 and are joined by tiny ridges at the base. Autumnal: All leaves are submersed, narrow and flat, 5 to 20 mm long, with inconspicuous white margins. Leaf tips have two lobes forming a U-shape; leaf bases clasp the stem but are not joined by ridges. Stem: Usually branched, rising to surface or sprawling. Flower: Tiny flowers lack sepals and petals and are located at the leaf bases on minute stalks. Pond: 2-4 tiny whitish bracts emerge from the flower base. Autumnal: bracts absent. Fruit: 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. Root: Fibrous, from plant base or sprouting from stem joints. Propagation: Plant fragments, seeds. Importance of plant: Provides forage and cover for young fish and aquatic insects. Ducks eat seeds and foliage. Distribution: Pond: Introduced from Europe; widespread in North America. Autumnal: North America. Habitat: Shallow water of lake margins and streams. May be confused with: Other water-starworts, including several species that may occur in Washington but are not included in this book. Due to the variability in leaf shape and size, mature fruits must be examined for positive identification of all water-starworts. Also confused with other opposite-leaved delicate plants when not in fruit, such as mudwort (Elatine) or horned pondweed (Zannichellia palustris). Photographs: Closeup of the floating rosettes of Callitriche stagnalis, closeup of Callitriche hermaphroditica. Line Drawings: See Callitriche heterophylla drawing
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