Stems viny, to 4 m, without cobwebby pubescence, nearly glabrous, or moderately pilose-pubescent proximal to nodes. Leaf blade mostly 1-pinnate, some simple; leaflets usually 4-8 plus additional tendril-like terminal leaflet, lanceolate to ovate, unlobed or 2-3-lobed, or most proximal 3-foliolate, 2-12 × 1-5(-6) cm, thin, not conspicuously reticulate; surfaces abaxially sparsely to densely pilose, not glaucous. Inflorescences axillary, 1-7-flowered; bracts well above base of peduncle/pedicel. Flowers broadly urn-shaped to bell-shaped; sepals pale lavender to reddish purple, grading to cream-yellow toward tip, ovate-lanceolate, 1.5-3 cm, margins not expanded, very thick, not crispate, tomentose, tips acuminate, recurved, abaxially sparsely to densely pubescent. Achenes: bodies silky-pubescent; beak 2.5-6 cm, plumose. 2 n = 16. Flowering spring-summer. Wooded cliffs and stream banks; 0-1400 m; Ala., Ark., Del., D.C., Ga., Ill., Ind., Ky., Md., Miss., Mo., N.C., Ohio, Pa., S.C., Tenn., Va., W.Va. The Fox Indians prepared a drink from the roots of Clematis viorna to use medicinally as a panacea (D. E. Moerman 1986).
From Flora of Indiana (1940) by Charles C. Deam
Infrequent to rare throughout the state except in the northern two tiers of counties where it is either absent or very rare. Clark's report from Marshall County is the only one from these counties. It is found mostly on the rocky, wooded slopes of streams. The leaves of this species, as of the next two [Clematis pitcheri and C. virginiana], are variable in the amount of the pubescence of the lower surface of the leaflets. Some are nearly glabrous while the majority are more or less densely pubescent. Plants with the apex of the leaflets long-acuminate are Clematis Ridgwayi Standley. I have a specimen of this form from Martin County named for me by Standley, and I have specimens from other counties which I refer to it.
Stem climbing, generally somewhat hairy at least at the nodes; principal lvs with 2-4 pairs of lfls, some of the lfls often trifoliolate; lfls lanceolate to ovate, entire or 2-3-lobed, thin, not prominently veined, generally hairy beneath and at the rachis-joints, not glaucous; cal urceolate; sep ovate or lance-ovate, 1.5-2.5 cm, caudate-acuminate, thinly hairy on the back, densely tomentose at the margins; style at anthesis hirsute, at maturity 3-5 cm, densely plumose throughout; 2n=16. Moist woods and thickets; Pa. to Ill. and Mo., s. to Ga. and Miss. (C. gattingeri; Viorna viorna; V. flaccida, a more hairy form)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.