This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Mostly handsome erect shrubs from Western and Southern Europe, North Africa, and the Atlantic islands. Leaves opposite, entire or toothed, oblong or lanceolate. Flowers large and showy, but very evanescent, and not opening in dull weather. Sepals 3 to 5. Petals white with a yellow or purple blotch at the base, or rose with a yellow spot at the base, never wholly yellow. Technically distinguished from Helian-tkemwm by the capsule being usually 5-valved, and the flowers cymose or solitary, seldom racemose. Etymology from the Greek name kiatos. Some of the species are tolerably hardy in the South of England.
1. G. ladaniferus (Fig. 41). - This has sessile 3nerved lanceolate leaves, glutinous above, and covered with a dense white tomentum beneath, and large white flowers with a purple blotch at the base of the petals. Native of Portugal, flowering in June. There are several varieties of it.
Fig. 41. Cistus ladaniferus. (1/3 nat. size.)
2. G. Cyprius. - Perhaps even commoner than the preceding, and often confounded with it. This has large solitary flowers and petiolate leaves, whilst in the former the flowers are borne in clusters of three or four on a common stalk, and the leaves are sessile.
3. G. laurifolius. - This is one of the hardiest species in cultivation, having petiolate 3-nerved ovate-lanceolate viscous leaves densely tomentose beneath, and white flowers. A robust growing shrub 6 or 7 feet high.
4. G. salvifolius. - A very variable species of slender habit. The variety generally met with in cultivation has ovate-lanceolate acute rugose nearly glabrous leaves on slender petioles, and medium-sized white flowers. A distinct species, about 3 or 4 feet high.
5. G. purpureus. - Leaves oblong or lanceolate, rugose, strongly veined, shortly petiolate, densely pubescent beneath. Flowers terminal, large reddish purple, with a dark blotch at the base of each petal. This is not so hardy as some of the foregoing.
6. C. Monspeliensis. - A very variable plant in the foliage, with small white flowers having yellow blotches about an inch in diameter. Young parts hairy and clammy. Leaves sessile, 3-nerved, strongly veined, linear or lanceolate, obtuse or acute.
7. G. populifolius. - A very distinct species of large stature with ovate-cordate acuminate rugose leaves on long petioles, and medium-sized white flowers tinged with yellow at the base of the petals. Pubescence slight, viscous. Flowers in lateral cymes.