Freshwater, monoecious or sometimes appearing dioecious, perennial herbs. Rhizomes absent. Stolons floating on or suspended in water, rooted or not. Roots usually branched with large root hairs. Leaves basal, emergent or floating, blade elliptic to orbiculate; apex obtuse to acuminate, base reniform or cordate; undersurface smooth on emergent leaves or with spongy, honeycomb-like aerenchymous tissue on floating leaves that covers most of the leaf undersurface; petiolate. Stipules 1 or 2, free or connate with petiole. Inflorescences cymose, sessile or short-pedunculate. Flowers unisexual, male and female flowers developing on the same or in different rosettes, developing 1 or 2 at a time within 1 or 2 bracts (collectively called a spathe), pedicellate, held above the water. Male flowers: sepals 3, free; petals 3, free, linear to lanceolate or oblanceolate, longer and narrower than sepal; stamens 6–12, filaments connate at least ½ their length or free for most of their length; anthers elongate or oval. Female flowers: sepals 3, free; petals absent or up to 3, free, linear to lanceolate, oblanceolate to petals broad-obovate; ovary of 3–9 carpels, with or without dissepiments; styles 3–9, 2-fid, divided from 1/4 to 1/9 of their length; ovules 5 –200 or more; staminodes 2–6, linear, not secreting nectar. Fruit a berry-like capsule, ellipsoid to spheric, smooth to ridged, dehiscing irregularly. Seeds ellipsoid, echinate, covered with blunt cylindric hairs or seeds tuberculate and without cylindric hairs.
A genus of 5 species worldwide, with 2 species in Australia (1 native and 1 introduced).
Recent molecular work (Li et al. 2022) has shown that Hydrocharis is rendered non mononphyletic by Limnobium, with Hydrocharis having nomenclatural priority.
Li, Z.-Z., Lehtonen, S., Gichira, A.W., Martins, K., Efremov, A., Wang, Q-F. & Chen, J.M.(2022). Plastome phylogenomics and historical biogeography of aquatic plant genus Hydrocharis (Hydrocharitaceae). BMC Plant Biol. 22(1):106.