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

Description Vegetative characteristics Trithuria austinensis is an annual herb with green to red, 20–40 mm long, linear leaves. Generative characteristics It is a dioecious speciesIles, W. J., Rudall, P. J., Sokoloff, D. D., Remizowa, M. V., Macfarlane, T. D., Logacheva, M. D., & Graham, S. W. (2012). Molecular phylogenetics of Hydatellaceae (Nymphaeales): Sexual‐system homoplasy and a new sectional classification. American Journal of Botany, 99(4), 663-676. and in large populations male and female plants occur at equal rates.Remizowa, M. V., Sokoloff, D. D., Macfarlane, T. D., Yadav, S. R., Prychid, C. J., & Rudall, P. J. (2008). Comparative pollen morphology in the early‐divergent angiosperm family Hydatellaceae reveals variation at the infraspecific level. Grana, 47(2), 81-100. The peduncles of the reproductive units ("flowers") are 10–50 mm long. In male plants, the 2-8 reproductive units consist of 2-4 4.2–7.2 mm long, and 1.0–3.0 mm wide bracts, and 3-15 stamens. In female plants, the up to 30 reproductive units are composed of 3-4 bracts, and 17-22 carpels. The bracts of the female reproductive units exhibit two different shapes.

Taxonomy Trithuria austinensis D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall was published by Dmitry Dmitrievich Sokoloff, Margarita Vasilyena Remizowa, Terry Desmond Macfarlane & Paula J. Rudall in 2008.Sokoloff, D. D., Remizowa, M. V., Macfarlane, T. D., & Rudall, P. J. (2008). Classification of the early‐divergent angiosperm family Hydatellaceae: One genus instead of two, four new species and sexual dimorphism in dioecious taxa. Taxon, 57(1), 179-200. The type specimen was collected by N. Gibson and M. Lyons in Austin Bay Nature Reserve, Australia on the 16th of November 1995.

Etymology The specific epithet austinensis refers to the type locality.

Ecology Habitat It has some tolerance towards salty water.Sokoloff, D. D., Remizowa, M. V., Macfarlane, T. D., Yadav, S. R., & Rudall, P. J. (2011). Hydatellaceae: a historical review of systematics and ecology. Rheedea, 21(2), 115-138.

Conservation It is not threatened. It is known from several populations.

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