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A climbing shrub of the Atragene section 6 to 8 ft high; young stems slightly ribbed, glabrous, becoming much enlarged at the joints with age. Leaves ternate, being composed of three leaflets on a common stalk 2 to 3 in. long; leaflets ovate or heart-shaped, 1 to 2 in. long, coarsely toothed or entire, with a little loose down about the veins and stalks when young. Flower solitary on a stalk about 3 in. long, purple or purplish blue, 2 to 3 in. across. Sepals four, thin, lance-shaped, pointed, prominently veined, downy, especially at the margins; sepals about 5⁄8 in. long. Seed-vessel surmounted by a feathery style about 11⁄2 in. long. Bot. Mag., t. 887.
Native of eastern N. America; introduced in 1797. It is most nearly allied to the European C. alpina, producing its flowers in May from the joints of the previous year’s wood, and having petals or petal-like organs between the sepals and stamens. It is, however, quite distinct in having but three leaflets to each leaf, and these have not the deep, handsome toothing of C. alpina. C. verticillaris is now very rare in gardens, as it is said to be also in a wild state.