Robert Francis Cox Naczi
Genus Description - Sep 5, elongate, imbricate in bud; cor 5-lobed to near the middle; stamens very short, inserted near the base of the cor; style slender, included, stigma capitate; capsule depressed-globose or globose. Aquatic herbs, the submersed lvs deeply pinnatifid into linear segments, the stem bearing an emersed, terminal, single (Eurasian sp.) or usually several (ours) scape(s), in ours the axis of each scape inflated, constricted at the joints, and distally bearing whorls (superimposed umbels) of bracteate fls.
Generic Diversity - 2 spp., the other (H. palustris L.) Eurasian