Fls trimorphically heterostylic; perianth blue to white, funnelform with bilabiate limb, the 3 lower lobes nearly or quite distinct, the 3 upper united about half their length, the middle upper lobe broader than the lateral and marked with yellow; stamens 6, inserted on the perianth-tube, the 3 opposite the lower lip exsert, those opposite the upper lip included and sometimes reduced or sterile; ovary 3-locular, one locule with a single pendulous ovule, the other 2 smaller and empty; nectaries septal; fr achene-like, enclosed within the accrescent perianth-tube, and beaked with the persistent style-base; marsh or aquatic herbs, often colonial, with broad or narrow lvs; infl a contracted spike-like panicle, the long stalk arising from the rhizome and bearing one lf with an expanded blade and above it a bladeless sheath. 3, New World.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.