Ruppia polycarpa is a submerged aquatic herb species in the genus Ruppia found in shallow brackish waters.

It is a common submerged herb on Australasian coasts, including Australia (NSW; SA; Vic; WA) and New Zealand (type locality).

[3] It was first described in 1967 by Ruth Mason from a specimen (CHR 150837B) found near the mouth of the Selwyn River, New Zealand, on the riverbed, on 27 February 1966 by J.

[2] It grows in "fresh to hypersaline coastal lakes, lagoons and estuaries".

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