Lithops

Lithops is a genus of succulent plants native to southern Africa. "Lithos" means "stone" and "-ops" means "face" in Ancient Greek; therefore "Lithops" means "stone-like". This is a very good description of these plants, which avoid being eaten by blending in with surrounding rocks.
They are relatively easy to grow if given sufficient sun and a suitable well drained-soil.
Normal treatment in mild temperate climates is to keep them completely dry during winter, watering only when the old leaves have dried up and been replaced by a new leaf pair. Watering continues through until the autumn when the plants flower and is then stopped for the winter.