CISTUS, a genus of the family Cistaceae. The members of the family live in dry, sunny places, especially on a sandy or chalky soil. There are 20 species in the Mediterranean region; many are cultivated ornamental shrubs, in English-speaking coun tries commonly called rock-rose. C. villosus and C. ladani f erns yield the resin ladanum, which is not to be confused with the hypnotic laudanum.