Clematis viorna L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - 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)