a white-flowered plant (Nasturtium officinale) of the crucifer family, growing generally in running water, as from springs: its leaves are used in salads, soups, etc.
See watercress in American Heritage Dictionary 4
(wôˈtər-krĕsˌ, wŏtˈər-)
noun
A pungent perennial Eurasian herb (Rorippa nasturtium-aquaticum) of the mustard family, growing in freshwater ponds and streams and used in salads and as a garnish.