Trithuria submersa is a species of plant in the family Hydatellaceae endemic to the Australian states New South Wales, South Australia, Tasmania, Victoria, and Western Australia.

[5] Individuals growing submerged in water are slender and green in colour.

[2] It is a monoecious species[6] with emergent, bisexual reproductive units ("flowers").

[10] Seed germination occurs in winter, once the seasonally dry habitat becomes wet.

[13][14] The specific epithet submersa, meaning "underwater", refers to the species aquatic habitat.