Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Clematis crispa' from the website Trees and Shrubs Online (treesandshrubsonline.
A deciduous, half-woody climber, varying from 3 to 8 ft high. Leaves pinnate, consisting of three, five, or seven leaflets; these leaflets are themselves often trifoliolate or variously lobed, but not toothed, varying from lance-shaped to broadly ovate with a heart-shaped base, and from 1 to 3 in. long by 1⁄3 to 11⁄2 in. wide, thin and glabrous. The larger leaves are altogether 6 to 8 in. long. Flowers solitary on stalks 1 to 3 in. long, fragrant; sepals 11⁄4 to 2 in. long, convergent below, spreading and separate towards the points, 1⁄3 to 1⁄2 in. wide, thin and wavy at the margins, partially downy at the back, bluish purple, nearly white at the margins. Seed-vessel either silky or becoming nearly glabrous. Bot. Mag., t. 1892.
Native of the south-eastern United States; introduced in 1726. This is regarded as one of the Viorna group, but is amply distinguished by the upper half of the sepals expanding widely and being much broadened and wavy at the margin. It flowers from June to August.