Watercress (Nasturtium officinale) is a fast-growing aquatic or semi-aquatic perennial. The hollow stems of watercress float on water. Watercress produces small white and green flowers in clusters.

This species is widely accepted as native from Europe to central Asia. The leading experts on the Brassica family, to which watercress belongs, have concluded that this plant also arrived in North America before European explorers, spread by migratory aquatic birds. For this reason, Jepson lists this plant as native; some other sources do not.

Watercress is sometimes quite aggressive in riparian environments in California. In some other states, it is classified as an invasive species.

Watercress is one of the oldest known leaf vegetables consumed by human beings. These plants are botanically related to garden cress and mustard, all noteworthy for a peppery, tangy flavor.