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A deciduous climber, growing 8 to 12 ft high. Leaves composed of three or five leaflets with downy stalks; leaflets ovate-lanceolate; 2 to 4 in. long, 11⁄4 to 21⁄2 in. wide, pointed, glabrous above, downy beneath. Flowers solitary on downy stalks without bracts; 4 to 6 in. across; sepals six to eight, long-pointed, wide-spreading, and more separated from each other than in C. florida (q.v.). In the typical C. patens the flowers are said to be white, but this is probably not in cultivation now, and the cultivated forms of the Patens group vary from white tinged with violet to deep violet-blue. Seed-vessels with silky tails.
Commonly cultivated in, and probably a native of Japan, whence it was introduced to Europe in 1836 by Siebold, who had found it in a garden near Yokohama. Also native of China. Some authorities regard it as a variety of C. florida; the distinctions are pointed out under that species.
C. patens has made its contribution to the formation of the large-flowered clematis hybrids, but the type was probably less used by breeders than the Japanese garden variety ‘Standishii’, introduced by Fortune in 1861. This is usually placed under C. patens, but is considered by some authorities to be a hybrid between that species and C. florida. The clematises which are customarily classed together in the Patens group flower in early summer on short shoots from the previous year’s wood and need no pruning apart from the removal of flowered growths.