Lithops species are probably amongst the most well camouflaged and cryptic plants in the world. Their common name, stone plant, is particularly apt, as they are often extremely difficult spot when they are growing nested amongst the gravel in their natural habitat. They are bizarre little plants that have a strange but fascinating beauty in their coloration and form that captures the attention of anyone who stumbles across them. Their ease of growth make them popular potplants and if well cared for, will make lifelong companions.

Description
Lithops plants consist of two fused leaves that form one head. Some species only ever have one head, like L. gracilidelineata, whereas other species such as L. olivacea can form big mounds of many heads with time. From ground level, the leaves taper down to a small, thin, carroty taproot that produces small adventitious roots when water is available. The size of one head ranges from 5-25 mm wide and from leaf surface to root tip, from 50-100 mm, depending on age. The windows of L. olivacea are completely clear, as in the picture, or they are lightly spotted with grayish flecks. L. olivacea bears a lovely yellow flower with a white centre late in the summer.

Distribution
Lithops occurs sporadically throughout all arid parts of the summer rainfall areas of South Africa and Namibia. The two varieties of L. olivacea, var. olivacea and var. nebrownii are restricted to Bushmanland, however, and are found most abundantly in the region of Aggeneys, Pofadder and Namies, although there are earlier collections far to the east from the Kakamas area, where it has not been seen in recent years. It is suspected that they may have been wiped out there due to the large-scale grape farming which has taken place.

Derivation of name and historical facts
The name Lithops is derived from the Greek lithos, a stone and ops, a face. L. olivacea was so named by Bolus in 1929 because of the olive green coloration of the epidermis. The first Lithops was "discovered" by Burchell in 1811 when he found what was at that time called Mesembryanthemum turbiniforme from the Prieska area.

Ecology
L. olivacea is a quartz lover and will always be found growing either on big outcrops of quartz or more commonly on quartz plains (vlaktes) where the quartz pebbles protect the plants from the blazing summer sun by reflecting a lot of the light and heat. Another succulent plant that is almost always found growing with L. olivacea is Avonia papyraceae, which loves the quartz too. When it is very dry, the plants shrivel and are almost invisible as they get covered with fine wind-blown sand. After rain, however, they absorb water and become fat and turgid.

Growing Lithops olivacea

Lithops plants, contrary to popular belief, are easy to grow. The small seeds can be sown in pots of fine, well-drained sand, any time during the summer months when temperatures are warm. Cover the seeds with a very fine layer of grit and water from below with a fungicide to prevent damping off. For the first 3-4 days cover the pots with a sheet of glass/clear perspex to keep the humidity levels high. Remove the glass and replace it with light shadecloth and mist once or twice a day for the next two weeks after which most seeds should have germinated. From then on mistings can be reduced to every second and then every third day as the little plants grow. At this stage it is not a good idea to flood the pot as this encourages lithops soup!

When the plants are a year old, water them once every two weeks in summer and once every 2 months (if necessary) in winter. When the new leaves are pushing though the old leaves, watering should be stopped altogether otherwise leaf pairs start stacking on top of each other. They need a bright spot to grow - somewhere that gets at least half a day of direct sunlight, otherwise they elongate and become ugly. Mealy bug is their worst enemy - if the 'white fluff' is found between the leaves, spray with an insecticide that has either Chlorpyrifos or Imidacloprid as an active ingredient. They do not need any fertilizer, but a weak solution from time to time won't do them any harm. If well loved and cared for they make lovely and fascinating pot plants.

References

• Cole, D.T. 1988. Lithops, flowering stones. Acorn Books, South Africa.
• Hammer, S. 1999. Lithops, treasures of the veld. British Cactus and Succulent Society.
• Nel, G.C. 1946. Lithops. University Press, Stellenbosch.
• Sprechman, D.L. 1970. Lithops. Associated University Press, New Jersey.

Adam Harrower
Kirstenbosch NBG
June 2003