Not to be semantically confused with : Hornbeam (Carpinus betulus), Yellow Horned-Poppy (Glaucium flavum), Red Horned-poppy (Glaucium corniculatum), Stag's-horn Clubmoss (Lycopodium clavatum), Horned Mustard (Sisymbrium polyceratium), Horned Pansy (Viola cornuta) nor with Horned Pondweed (Zannichellia palustris) another weed of water.

Uniquely identifiable characteristics

Distinguishing Feature : It is distinguished from other underwater plants by the whorls of bifurcated linear and cylindrical leaves.

The plant does (only sometimes) have flowers; it is monoecious with separate but really tiny male and female flowers both appearing at different nodes on the same plant. The male flowers are about 1mm long have between 10 to 25 stamens. The female flowers are just over 1mm long have a single-celled ovary with just one style (which is minutely bifurcated at the end into 2 stigmas) and one ovary. The fruits are smooth or slightly warty with a beak and usually with two long spines at the base but this feature can be missing (on var. inerme) or can be replaced by tubercules (on var. apiculatum).

It occurs locally frequent in still freshwater, or in ditches, lakes, ponds, canals or slow rivers.