Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Clematis acutangula' from the website Trees and Shrubs Online (treesandshrubsonline.
A deciduous climbing shrub 12 to 15 ft high, perhaps more, with slender stems sharply angled, and very viscid when young; reddish purple. Leaves doubly pinnate, 6 to 9 in. long; the primary divisions are three-foliolate, or, in the case of the lower ones, often five-foliolate; leaflets ovate-lanceolate, 1 to 2 in. long, coarsely toothed or two- or three-lobed, glabrous and shining on both surfaces, and of a purplish tint; leaf-stalks ribbed, the bases of each pair flattened, expanded, and surrounding the stem. Inflorescences 11⁄2 to 3 in. long, with usually five flower-buds, the terminal one of which opens first, and is often the only one to open. Flower bell-shaped, 1 in. wide, 5⁄8 in. long; sepals four, lilac-coloured, narrowly ovate, but much curled back at the points, which are downy. Stamens and styles clothed with silky down.
Native of the Himalaya and China; introduced from the latter by Wilson for Messrs Veitch about 1903. The only plant I have seen, and the one from which this description was made, grew in the Coombe Wood nursery, where it was a luxuriant grower and quite hardy, flowering in autumn.