Floating herbs. Fronds asymmetrical with 3-15 nerves, discoid or reniform to obovate, in groups of 2-5, flat or distinctly inflated with a 2-lobed prophyllum at the base; raphides and druses present. Slit of the budding pouch lateral to the margin of the frond, remaining attached to the parent by a slender stipe. Roots 2-18, usually from the swollen portion beneath the fronds. Flowers rarely produced, enclosed in spathe; 2 male and 1 female flower in a lateral slit pouch; each male flower with 1 stamen; anthers 4-thecous; 1-4 ovules in pistillate flowers.