Stems usually ascending to erect, occasionally somewhat viny, 0.6-1 m, glabrous. Leaves all simple, blade often 1-pinnate on distal and middle leaves on vigorous plants 4-13 × 2-9.5 cm; leaflets 2-6 plus additional tendril-like terminal leaflet, ovate, unlobed, 1.5-6 × 1-4.5 cm, not prominently reticulate; surfaces abaxially glabrous and glaucous. Inflorescences terminal and axillary, flowers solitary. Flowers ovoid to broadly urn-shaped; sepals purple or reddish purple, whitish toward tips, ovate-lanceolate, 1.2-2.5 cm, margins not expanded, thick, not crispate, tomentose, tips acute, spreading, abaxially glabrous. Achenes: bodies puberulent; beak 2.5-3.5 cm, plumose. 2 n = 16. Flowering spring-early summer. Calcareous, dry woods, glades, rock outcrops; of conservation concern; 200-600 m; Va. Clematis addisonii is known only from Botetourt, Montgomery, Roanoke, and Rockbridge counties in western Virginia. Reports of this infrequent species from other southeastern states have been based on misidentified specimens (W. M. Dennis 1976).
Stem at first erect, but often soon becoming procumbent or scrambling, to 1 m long; herbage glabrous and glaucous; lvs thin, not strongly reticulate; the simple ones broadly ovate, subsessile, obtuse and mucronate, the compound ones (when present) appearing later, especially on the branches, with 2(3) pairs of round-ovate lfls, the lowest pair much exceeding the upper; cal urceolate; sep narrowly ovate, 1.5-2.5 cm, glabrous on the back, tomentose on the margins distally; mature style 2.5-3.5 cm, strongly plumose; 2n=16. Dry limestone hills; w. Va. Apr.-June, July.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.