Trithuria austinensis is a species of aquatic plant in the family Hydatellaceae endemic to Western Australia.

[1] Trithuria austinensis is an annual herb with green to red, 20–40 mm long, linear leaves.

[2] It is a dioecious species[3][2] and in large populations male and female plants occur at equal rates.

In female plants, the up to 30 reproductive units are composed of 3-4 bracts, and 17-22 carpels.

[2][1] The type specimen was collected by N. Gibson and M. Lyons in Austin Bay Nature Reserve, Australia on the 16th of November 1995.