Rhizomatous; stems to 1 m, the upper part densely and softly villosulous with very slender hairs 0.2-0.3 mm, with or without a few scattered longer bristles; lvs ovate-lanceolate to ovate, 2-6 cm, minutely villosulous on both sides; lower axillary cymes on long ascending peduncles, the upper peduncles progressively shorter, forming a terminal pyramidal panicle; sep lanceolate or lanceolate-linear, 6-9 mm, ±glandular-villous; cor 11-17 mm; styles and stamens 10-15 mm; capsule ca 5 mm thick, hispidulous; 2n=20. Swamps and wet woods; w. Ky. and s. Mo. to Tex. and Ga. July, Aug. (Nama o.) Hybridizes with no. 2 [Hydrolea uniflora Raf.].
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.