Xi Yang Cai

Nasturtium officinale W.T.Aiton (Brassicaceae), watercress, called Xi Yang Cai ("Western ocean vegetable") in Chinese for its European origin, is a perennial aquatic or semi-aquatic herb with hollow, succulent, creeping or floating stems 20-90 cm long rooting at the lower nodes in slow-moving freshwater streams and springs. The leaves are alternate, pinnately compound with 3-9 ovate to oblong leaflets, the terminal leaflet largest, all dark glossy green, slightly fleshy, and pungent. Small four-petalled white flowers, 4-6 mm across, are borne in terminal racemes that elongate in fruit, followed by slender curved siliques 1-2 cm long containing two rows of small reddish seeds. Native to Europe and West Asia and now naturalised worldwide, watercress is widely cultivated as a salad green in China. In southern Chinese folk and TCM-adjacent practice, the fresh whole herb is used to clear lung heat, moisten dryness, cool blood, promote urination, and relieve cough; it is also valued nutritionally for vitamin C and glucosinolates.