Perennial aquatic herbs, emergent, rarely submerged; rhizomatous, usually with tuber-bearing roots. Leaves basal, narrow, more or less flat and strap-like, often thickened and spongy basally, (6–)40–450 cm long and c. 4 cm wide; basal sheath open, without a ligule. Inflorescence few–many-flowered, racemose, often spike-like, terminal on a prominent scape. Flowers bisexual; perianth of 2 similar whorls of 3 segments, each segment falling with its attached stamen after anthesis; stamens 6, each with a 2-locular, subsessile anther; ovary superior, usually of 3–6 fertile carpels but irregularly 2–8, each carpel with one ovule; style short and stigma often recurved. Fruit dehiscent or indehiscent, the carpels readily separating. Seed 1 per carpel.
8 species all endemic to Australia; 6 in Victoria.
Cycnogeton has recently been resurrected following molecular and morphological studies finding some taxa previously included in Triglochin (i.e. Triglochin procera R.Br. and allied taxa) to be clearly distinct from other Triglochin species. These two genera are principally distinguished by the presence of woody rhizomes and tuberous roots, absence of ligules on basal sheaths, absence of carpophore and sterile carpels, and lack of hooked appendages of fruits in Cycnogeton.