Small, submerged or partly emergent aquatic herbs, ephemeral. Stem reduced. Leaves tufted at base, alternate, slender and subterete to ± flattened; sheath absent. Inflorescence apparently a reduced cyme with several unisexual flowers arranged in an umbel-like cluster (often interpreted as a head), terminal, subtended by 2–several primary bracts. Flowers with perianth absent, not separated by secondary bracts. Male flower of 1 stamen. Female flower with unknown number of carpels, possibly 3 and fused in Trithuria; ovary with 1 locule and 2 or 3 (Trithuria) or 5–10 (Hydatella) styles; ovule 1. Fruit small, dry, a capsule opening by 3 valves (Trithuria) or indehiscent (Hydatella); seed 1; endosperm almost absent.
2 genera (Hydatella and Trithuria) with about 8 species occur in Australia and New Zealand; only Trithuria occurs in Victoria. These 2 genera have been often included in the Centrolepidaceae on the basis of their habit.
The inflorescence is here interpreted as being an umbel-like cluster of unisexual flowers because the ovaries are stalked. It is not known if the stalk represents the stalk of a carpel, hence female flower, or if it is the stalk of the ovary of a sessile flower. Likewise, the number of carpels is not known (Hamann 1976).