Atragene americana Sims; Clematis verticillaris de Candolle; C. verticillaris var. cacuminis Fernald; C. verticillaris var. grandiflora B.Boivin

Stems ± viny, climbing or trailing, 0.25-3.5 m. Leaves: leaflets unlobed or occasionally 1-3-lobed, (2-)3-6(-10) cm, margins entire or shallowly crenate-serrate. Flowers: sepals remaining moderately divergent, reddish violet, ovate to oblong-elliptic, 2.5-6 cm, margins not fluted, tips rounded-mucronate to nearly acuminate. 2 n = 16.

Flowering spring. Calcareous cliffs, rock ledges, talus slopes, gravelly embankments, rocky woods, and clearings; 0-1300 m; N.B., Ont., Que.; Conn., Del., Ill., Iowa, Maine, Md., Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Pa., R.I., Vt., Va., W.Va., Wis.

Clematis occidentalis var. occidentalis formerly occurred in Ohio. Plants in the western part of the range of this variety tend to have larger, more abruptly tapering sepals; they have been segregated as var. grandiflora B.Boivin, but they do not appear to constitute a distinct taxon.