Posidonia coriacea is a species of seagrass that occurs in the southern waters of Australia.

This species is found at depths from 1 to 30 metres on white sands, in areas subject to intense wave action.

The leaf sheath breaks into strips, rather than the fibrous detritus of similar species.

This species is contained by the Posidoniaceae family, one of eight occurring in southern Australia.

The ninth member, Posidonia oceanica, is found in the mediterranean sea.