Trithuria is a genus of small ephemeral aquatic herb that represent the only members of the family Hydatellaceae found in India, Australia, and New Zealand.

[3][4] Until DNA sequence data and a reinterpretation of morphology proved otherwise, these plants were believed to be monocots related to the grasses (Poaceae).

They are unique in being the only plants besides two members of Triuridaceae (Lacandonia schizmatica and L. braziliana) in which the stamens are centred and surrounded by the pistils; in Hydatellaceae the resulting 'flowers' may instead represent condensed inflorescences or non-flowers.

[6] Together, these three families compose the order Nymphaeales in the APG III system of flowering plant classification.

Trithuria exhibits a remarkable similarity to Centrolepis and species of both genera were mistaken for members of the other genus.

was described[3] without a type designation[10] by Georg Hans Emmo Wolfgang Hieronymus based on previous work by Ferdinand von Mueller.

),[16] which is placed in the order Poales Small[17] but it was separated as its own family Hydatellaceae U.Hamann by Ulrich Hamann in 1976[18][13][19] with Hydatella Diels as the type genus.