Sp. Pl. 1: 543. 1753.
Stems viny, to 3 m, glabrous or sparsely to moderately pilose-pubescent, denser at nodes. Leaf blade 1-2-pinnate or rarely a few simple or 3-foliolate; leaflets 4-10 plus additional ± tendril-like terminal leaflet, usually lanceolate to ovate, occasionally linear, unlobed or proximally 3-5-lobed, (1.5-)3-10 × (0.1-)0.4-4(-5) cm, thin, not conspicuously reticulate; surfaces glabrous, not glaucous. Inflorescences terminal, 1-flowered; bracts absent. Flowers bell-shaped; sepals distally strongly spreading to recurved, violet-blue, lanceolate, 2.5-5 cm, margins proximally thick and tomentose, distally broadly expanded, 2-6 mm wide, thin, crispate, less conspicuously tomentose than proximal portion, or glabrate, tips acuminate, abaxially glabrous. Achenes: bodies appressed-puberulent; beak 2-3.5 cm, appressed-puberulent. 2n = 16.
Phenology: Flowering spring–summer.
Habitat: Low woods, bottomlands, swamps
Elevation: 0-200 m
Ala., Ark., Fla., Ga., Ill., Ky., La., Miss., Mo., N.C., Okla., S.C., Tenn., Tex., Va.
Clematis crispa is highly variable in leaflet width, and conspicuous variation may occur on a single plant (R.O. Erickson 1943); no discontinuity or geographic correlation exists that would permit the recognition of varieties. The dilated, petaloid sepal tips and thin, crispate, broadly expanded sepal margins are diagnostic for this species.