Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Cistus × purpureus' from the website Trees and Shrubs Online (treesandshrubsonline.
A bush of rounded habit 3 to 4 ft high, and as much through; young branches downy and resinous. Leaves oblong-lance-shaped to obovate; 1 to 2 in. long, 3⁄8 to 5⁄8 in. wide; blunt at the apex, tapering at the base but scarcely stalked, the bases clasping the stem; upper surface dull greyish green, the veins sunken; the lower one pale with starry down. Flowers 21⁄2 to 3 in. across, reddish purple with a conspicuous dark red blotch at the base of each petal; the flowers are borne in terminal clusters of about three. Sepals ovate, with short slender points and covered with starry down.
This fine rock rose, by far the best of its colour in cultivation, is considered to be a hybrid between C. creticus, whence it gets its colour, and the spotted form of C. ladanifer, from which it derives its greater size and conspicuous blotches on the petals. It is only hardy through comparatively mild winters.