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

Male plants produce reproductive units with 10–11 mm long peduncles, 5–9 bracts and 9–11 stamens.

The 0.2–0.25 mm long fruits with a three-ribbed pericarp bear smooth seeds.

[1] It was published by Dmitry Dmitrievich Sokoloff, Margarita Vasilyena Remizowa, Terry Desmond Macfarlane, and Paula J. Rudall in 2008 based on previous work by David Alan Cooke.

[3] Under the Biodiversity Conservation Act 2016, it is classified as a Priority 1: Poorly-known species.