Perennial herb 6 - 20 cm tall Stem: submersed or free-floating. Leaves: submersed, 1 - 5 cm long, often two-parted at base, each segment forking several times, progressively getting shorter and narrower toward tip, end segments circular in cross section, the central axis (rachis) becoming zigzag or indistinct. The leafy branches float beneath the water surface and have numerous well-developed bladders that are often dark red to black and more than 2 mm across. Flowers: borne six to twenty on a stalk (scape) 1 mm or more in diameter, subtended by bracts, yellow petals are two-lipped with upper and lower lip nearly equal in length, lower lip having a half-spherical projection. The spur (extended sac at base of petals) is two-thirds as long as the lower lip, curving forward. Fruit: a two-valved capsule on recurved stalks, containing small seeds.
Similar species: Utricularia radiata, Utricularia intermedia, Utricularia minor, Utricularia geminiscapa, and Utricularia gibba are other aquatic or amphibious Utricularia species with dissected leaves. The flower stalk of Utricularia radiata has a whorl of leaves with inflated petioles. Utricularia intermedia and U. minor have flat leaf divisions. Utricularia geminiscapa and U. gibba have flower stalks less than 1 mm across, inflorescences with fewer than four flowers, and leaves with bladders less than 2 mm across.
Flowering: late May to mid September
Habitat and ecology: Locally common in shallow water.
Occurence in the Chicago region: native
Etymology: Utricularia comes from the Latin word utriculus, meaning "a small bottle."This refers to the insect-trapping bladders on the leaves and runners of the bladderworts. Macrorhiza means "having large roots or root stocks."
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.