Submersed, free-floating; lvs numerous, 1-5 cm, mostly 2-parted at base and then repeatedly and unequally (quasipinnately) dichotomous, the segments terete, progressively narrower, the ultimate ones filiform and strongly acuminate; bladders numerous, on the lvs; peduncles emergent, 6-20 cm, with 1-several scattered bracts below the infl; fls mostly 6-20 in a lax raceme, yellow, the lower lip mostly about equaling the upper, slightly lobed, 1-2 cm, with well developed palate; spur falcate, directed forward, two-thirds as long as the lower lip; pedicels arcuate- recurved in fr; 2n=44. Quiet water; circumboreal, s. to Fla. and Calif. June-Aug. (U. macrorhiza)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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