White watercress (Rorippa nasturtium-aquaticum syn. Nasturtium nasturtium-aquaticum, Nasturtium officinale, Sisymbrium nasturtium-aquaticum)
Family name: Mustard family (Brassicaceae)
Native range: Europe
General: Aquatic or semiaquatic perennial. White watercress can grow while submerged or prostrate on wet soil. The stems root from the nodes. Stems hollow.
Leaves: Alternate, nearly toothless, pinnately lobed with 3 to 9 leaflets. The terminal leaflet is larger than the side ones. Leaflets oval shaped.
Flowers: White, small, 0.2 inches wide, 4 petalled flowers borne on long stems, appearing April through September.
Fruit: Slender pods are about 0.4 to 0.6 inches long. The seeds within the pod are small and are contained in two rows.
Look-alikes: Onerow yellowcress (Rorippa microphylla), a non-native, is very difficult to distinguish from white watercress in the field. They both occur in moist soils and behave similarly. Onerow yellowcress seed appear in one row in the pod and a slightly larger and more prolific than white watercress seeds.
Habitat: Lakes, ponds, rivers, streams, springs, moist ground
Threats to native habitats: White watercress rapidly forms dense stands that exclude native plants. It is highly threatening to natural plant communities. All detected occurrences should be eradicated.
Commercial Availability: White watercress is an edible green that is widely cultivated.