Fls half-epigynous, with a shortly prolonged hypanthium, mostly 5 in a compact, head-like terminal cyme; sep of the central fl commonly 2, of the lateral ones 3; cor rotate, that of the central fl regular and commonly 4-lobed, that of the lateral ones slightly irregular and commonly 5-lobed; stamens paired at the sinuses of the cor, each bearing a single pollen-sac; carpels several, most often 4 in the central fl and 5 in the lateral ones, united to form a compound ovary with distinct styles and capitate stigmas. Monospecific.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.