About 10,000 species of succulents exist in the world. Six families house most of them: Asclepiadaceae, Asphodeliceae, Cactaceae, Crassulaceae, Euphorbiaceae, and Mesembryanthemaceae.

This discussion focuses on the family Mesembryanthemaceae, generally, and the genus Lithops, specifically. The family Mesembryanthemaceae, more conveniently known as the Mesembs, encompasses numerous species characterized by chiefly southern African fleshy-leaved herbs or subshrubs.

Family members include Cheiridopsis, Conophytum, Dinteranthus, Fenestraria, Frithia, Lampranthus, Lapidaria, Mestoklema, Monilaria, Nananthus, Pleiospilos, Titanopsis, Trichodiadema, and our subject genus, Lithops.

John Burchell discovered living stones in 1810 or 1811 when he picked up a curiously shaped stone in South Africa only to find it to be a plant. Originally classified as Mesembryanthemum turbuniformis, it became Lithops turbuniformis when the Mesembs were reevaluated and classified into different genera. As currently revised by D. T. Cole in Lithops - Flowering Stones, there are over 145 varieties, forms, and cultivars representing 36 species.

In habitat, living stones extend in a large area in widely separated sparsely populated colonies. They are largely found in South Africa, and the west coast of West Africa and Namibia, almost to Angola, also supports populations. Very arid (about two inches of rainfall per year!), desolate areas make up the typical habitat, though some species populate the grassveld and other areas where ample water and nutrients exist.

The plants mimic their natural surroundings to an astounding degree. They are masters of camouflage; in periods of drought (almost all the time) they shrink below the soil level. Some researchers have concluded that living stones develop "contractile" roots, which they use to pull themselves down into the soil. Others disclaim this conclusion and attribute the characteristic to extreme shriveling and subsequent covering by blowing sand and soil. At any rate, the casual collector in the field is highly unlikely to spot the plants.

Despite their near invisibility in habitat, living stones have become quite popular among collectors of succulents. Their strange resemblance to rocks and stones combined with their intricate markings and space-saving size has led to a surging demand. This popularity has resulted in a growing list of cultivars, which has occurred with cultivation of aberrants.

A single living stone plant consists of two succulent leaves attached at the outer edges with a fissure between them, attaining heights from 1/2 to 1 inch and widths from 1 to 3 inches. The two leaves are fused below the fissure, and above the leaves' junction with the rootstock grows an internal new body, called a meristem. In habitat (when flush with the ground) all light enters through the windowed leaf tips. Once a year, at least one new body develops from the meristem. After the plant flowers, it goes into a period of dormancy, and the old leaves provide nourishment to the new. With this nourishment, the new body begins to push out from the fissure. The fissure of the new leaves forms at about 90 degrees to the old fissure. Eventually, the old leaves will remain only as dry skins on the sides of the new bodies. Sometimes, the old body does not dry up and wither, remaining on the side of the new generation. This condition indicates over-watering and too much shade.

Lithops flowers, which appear in fall, are daisy-like with colors varying with species. White, yellow, or sometimes peach colored flowers emerge from the fissure. The coloration of the leaf-faces varies widely, even within species, making identification problematic. The leaf-faces have colored dots or lines marking them, with dimples or indentations where the markings appear. Sometimes the markings heavily cover the leaf-faces, and sometimes the windows cover most of the leaf-faces. Variations occur everywhere between the extremes. Some species form multi-headed plants, others have only a single head of paired leaves.

Lithops, the word, is derived from combining two Greek words: lithos, meaning stone, and opsis, meaning face or appearance. In Africa, farmers call the plants beeskloutjies (cattle hoof) or skaappootjies (sheep foot). The plants are so hard to spot in habitat that often farmers don't know they have them on their farms. This leads to the probability that additional species remain to be discovered. It also raises concerns that their natural habitat is being reduced and destroyed by farming and development activities.

In cultivation, living stones require well-drained soil, much the same as cactus. They grow slowly, thrive in bright full sun, tolerate temperatures from cool to intense heat, and require very little water. Typically, growers keep the bodies above the surface of the soil, a departure from their natural habitat condition. They have an extensive root system, which requires a larger pot than the plant size would indicate.

The health of living stones in cultivation depends on soil drainage, sufficient bright light, and proper watering. Over-watering is the chief cause of early demise, causing the leaf bodies to burst. Other health concerns are soft rot and mealybugs.

Watering is critical. In the warm growing season (starting in March), when the leaves start to shrivel, drench the soil then leave it to dry out completely. Two or three days after it has dried completely, water again. Stop watering altogether during the cold season (beginning at the end of November), but mist once every two weeks. Once the old leaf pair has withered entirely, resume the watering schedule.

Living stones need four to five hours of daily direct sun and dry air conditions. Growers should take care when first introducing the plants to sun as they sunburn easily. Windowpanes can magnify the sun and should be taken into consideration when assessing the total hours of sunlight. The plants etiolate when they receive too little light, growing tall and out of proportion.

Living stones can be propagated by separating clumps of heads, but the predominant method is by growing from seed.

BIBLIOGRAPHY

Miles Anderson, Cactus and Succulents, Illustrated Encyclopedia (Lorenz Books, 1999)

Ed Storms, The New Growing the Mesembs (Ed Storms Inc., 1986)

Webster's Ninth New Collegiate Dictionary (Merriam-Webster Inc, 1999.

Lance & Kerri's World of Lithops

Lithops, Dr. Leonard Perry, Professor, University of Vermont, PSS123 course, Fall 1997.

The Chinle Cactus and Succulent Club