Description from Flora of China
Plants perennial or annual, in saline, brackish, or extremely hard water, totally submerged. Rhizomes slender, usually branched. Stems terete, elongated or not. Leaves alternate, sessile, narrowly linear, entire or minutely denticulate toward apex; stipules adnate to leaf base and sheathing stems; sheaths shortly auriculate, ligule absent. Inflorescences of few-flowered spikes, pedunculate; spikes enclosed by involucral leaves at first; peduncles short at first but elongated in fruit. Flowers hermaphroditic, small, ebracteate. Perianth absent. Stamens 2; anthers sessile, extrorse, opening by longitudinal slits. Carpels 4 or more, free, 1-ovuled, sessile in flower but usually becoming narrowly stipitate in fruit; stigma sessile, peltate or umbonate. Fruit drupaceous, asymmetric, indehiscent. Seeds without endosperm.
Guo Youhao & Li Qingyi. 1992. Ruppia. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 83-85.
One genus and three to ten species: salt marshes throughout temperate and tropical regions; one species in China.
(Authors: Guo Youhao (郭友好); Robert R. Haynes, C. Barre Hellquist)