Submerged or with some leaves floating, annual or perennial, aquatic herbs; rhizomes rooting at nodes. Leaves alternate or opposite, distichous, usually sheathing at base; ligule sometimes present. Flowers solitary or forming terminal, spike-like inflorescences; initially enclosed by a subopposite pair of leaves or a leaf sheath. Flowers bisexual or unisexual, very small; bracts present or absent; perianth absent or of 3 or 4 scales, rarely fused and cup-like; stamens 1– 4, anthers sessile or on filaments, anthers sometimes fused to form a single anther mass; pollen ± spherical or reniform; carpels (1–)3(–9), free; ovary ± ovoid; stigma ± sessile and peltate or on a long slender style. Fruit usually aggregate, drupe-like with outer tissues membranous or spongy, inner tissues usually hard and bony, or an achene; seed without endosperm.
6 or 7 genera with c. 90–110 species worldwide; 4 genera in Australia and Victoria.
Lepilaena and Zannichellia have previously been included in Zannichelliaceae. Historically, Potamogetonaceae and Zannichelliaceae have not been considered closely related as they share few morphological characters (Les & Pippery 2013). Recent molecular studies have found a strong relationship between Potamogetonaceae and Zannichelliaceae, and the latter is now included in Potamogetonaceae.
In Potamogeton the presence of perianth appears open to interpretation. Scales united to the anthers may represent perianth, or to be associated with the anthers. Recent treatments have suggested these sepaloid scales constitute perianth (Papassotiriou et al. 2011). This position has been followed in the current treatment. The previous Flora of Victoria treatment interpreted these scales as arising from anthers, with perianth regarded as absent. In that treatment, Potamogetonaceae included Potamogeton and Ruppia, and the absence of perianth was used as a character to unite these two genera. Ruppia is now treated in a separate family. See note under Ruppiaceae.