The character of leaves spirally arranged seems not to be true for Hippuris spiralis. In fact, in that entity the leaves are whorled but the whorls are oblique. This variation may be caused by twisted shoots, especially in running water. Terminal subshoots are a common variant in H. vulgaris. For these reasons, both H. spiralis and H. vulgaris var. ramificans are treated here as synonyms of H. vulgaris.