Rhizomes pink, freely branching, producing extensive clumps, 2-3 cm diam., with fibrous remains of old leaves; roots fleshy. Stems usually 1-branched, solid, 7-15 dm. Leaves: basal deciduous, at first erect, then recurved, blade dark green, with prominent median thickening, 4-10 dm × 2-3 cm, slightly glaucous basally; cauline equaling inflorescence unit. Inflorescence units 4-12-flowered; spathes green with brown margins, outer spathe strongly keeled, inner without keel, 6-9 cm, subequal, margins not scarious. Flowers: perianth bright yellow; floral tube 0.6-0.8 cm, with no constriction into ovary; sepals bright yellow or cream colored, lanceolate to ovate or suborbiculate, 5-7.5 × 3-4 cm, base abruptly attenuate, claw ca. 1/2 length of limb, signal a darker yellow basal patch limited by short, brown lines; petals without veining, lanceolate to spatulate, 2-3 cm; ovary triangular in cross section with concave sides and narrow groove at each angle, 1.5 cm; style keeled, 3-4 cm, crests spreading, 1-1.2 cm, laciniate at apex; stigmas rounded with prominent tongue; pedicel 2.5-7 cm. Capsules prismatic to oblong-ovoid, obscurely 3-angled with obvious groove at each angle, 3.5-6 cm, beak 5 mm. Seeds D-shaped, flattened, 6-7 mm, corky, lustrous. 2n = 34. Flowering Apr--Jun. Swamps, wet shores of rivers and lakes; introduced; B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Ala., Ark., Calif., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Mass., Miss., N.H., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Va., Wash., W.Va.; Eurasia, n Africa.