[4] Posidonia australis reproduction usually occurs through sexual or asexual methods but, under extreme conditions, by pseudovivipary.

[6] In 2022, a study by the School of Biological Sciences and Oceans Institute at The University of Western Australia showed that a single plant of this species can grow vegetatively by using rhizomes to cover an extensive area, similar to buffalo grass.

In Western Australia it occurs in the Shark Bay region, around islands of the Houtman Abrolhos, and southward along the coast of the Swan Coastal Plain.

The species is recorded at the edge of the Esperance Plains, the Archipelago of the Recherche, at the southern coast of the southwest region.

[4] A sign of a nearby occurrence of Posidonia is the presence of masses of decomposing leaves on beaches, forming fibrous balls.

A research article in the Proceedings of the Royal Society[8] reported in June 2022 that genetic testing had revealed that samples of Posidonia australis taken from a meadow in Shark Bay up to 180 km (110 miles) apart were all from a single clone of the same plant.

The genus name for this species, Posidonia, is given for the god of the seas Poseidon, and australis refers to the southern distribution.