The living stones (Lithops N.E. Brown) are odd succulents native to deserts and sparse, dry shrub and grasslands of sub-Saharan Africa. The plants are members of the Aizoaceae (Ficoidaceae), the carpetweed or fig-marigold family. Depending upon the authority, Lithops has 35 to 40 species, but over 145 varieties and forms. To confuse matters, a variety or form of one Lithops species may look almost identical to a variety or form of another species and two closely related varieties often look completely different.

In their native habitat where annual rainfall ranges from 10 centimeters (4 inches) to 50 centimeters (10 inches), Lithops are subterranean with only the surfaces of the succulent leaves exposed. Besides their low rounded profile, the epidermis of the exposed leaf contains specialized cells, idioblasts, which contain colorful tannins. Often growing in pebbly soils, colonies of Lithops appear like little stones among all the other rocks. They were named by Nicolas Edward Brown in 1922 from the Greek lithos, stone, and –opsis, appearance.

The tannins primary purpose was probably to protect the plant from intense solar radiation. The side-effect of coloring the plant to look like a rock, and hence hiding it from herbivores, made the plant more successful.

The meristem or growing tip is located low between the two leaves. At the start of the dry season, Lithops bloom—a single white, yellow, or pinkish-brown daisy-like flower emerges from the slit between the two leaves. After the plant flowers, the two succulent leaves shrivel; their moisture and nutrients are pulled back into the plant and sent into the developing leaves. Each year's leaves are arranged 90 degrees to the previous year's leaves. Because of the dry climate, the old leaves can build up around the plant and provide a means of estimating the plant's age.

The photographed plant (possibly Lithops gesinae var. annae) is 2.0 centimeters (<1 inch) across and appears over-potted in a 5 centimeter (2 inch) pot. The body of a living stone is conical with the widest part, the thick fleshy paired leaves, upright. The small, yet oversized-appearing pot accommodates the plant's extensive root system. In cultivation, the plants are potted high to prevent rotting and to expose their unique structure.

(Compiled from: Hortus Third, Staff of the L.H. Bailey Hortorium, NY State College of Agriculture and Life Sciences, Cornell University, Macmillan Publishing, NY, 1976; W3TROPICOS, Jim Solomon, Missouri Botanical Garden; "The Living Stones, I Presume", David Kennedy, Chinle Cactus and Succulent Club, Cooperative Extension Service, Colorado State University, 2003)