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Best known as the stone plants from Southern Africa that have fused their leaves together to conserve water and appear as unlike a plant as possible.
In the drier areas of Southern Africa, a family of leaf succulents has developed some unique ways to survive on the tiniest amounts of water, avoid being eaten by thirsty animals, and even to release seed only when conditions are right for it to germinate. The best known of these is the Lithops. Flowering StonesLithops have no spines, no poisons, and no tough bark or skin. They are simply two highly succulent leaves fused together and mostly buried in the ground, with a translucent top window to allow some light to reach the green interior for photosynthesis. They have patterned and coloured top surfaces similar to those of stones in the surrounding area and only a dedicated search will find them unless they are in flower. In the dry season they may shrink so much that they disappear below ground level. The appearance of an attractive pebble, a pebble which will produce bright daisy flowers each autumn, has made Lithops a popular cultivated plant. No two plants even of the same species have exactly the same patterns and there are many varieties to select from. The habit of growing embedded in the ground reduces water loss but also reduces the ability of the plant to take in carbon dioxide and so slows growth. Crassulacean Acid Metabolism (or CAM) is also used, which means that the stomata on the leaves are tightly closed all day to reduce water loss, only opening when it is cool at night to store carbon dioxide for photosynthesis the next day. This reduces water loss by 90% or more compared to normal plants but also reduces the growth rate because only a little carbon dioxide can be stored. So Lithops are slow growing plants that can only compete in the harshest environments where other plants cannot survive. Luckily for the Lithops, there are a great many dry rocky hillsides in South Africa and Namibia and over 30 species are found over a huge area, if you have excellent eyesight! Lithops have fascinating seed capsules formed in sections, each with a lid which opens when it becomes wet. A raindrop will then wash out a few seeds, hopefully to germinate in the rare shower. Most seed falls to the ground very close to the mother plant to take advantage of favourable spots in the harsh terrain. Fully ripe seed will germinate in just a few days if it is warm and wet. Once it dries out, the lid will close again to wait for the next passing thunderstorm. Growing PebblesSo if Lithops can survive heat and sun and little or no rain, even sometimes surviving freezing winter conditions, they should surely be tough enough to survive in a pot. Unfortunately for many people they rapidly die, usually dissolving into green slime, sometimes turning white and slowly drying up over weeks or months. But by following some fairly simple rules, Lithops are not difficult to keep alive and even to flower. Lithops have a strong annual lifecycle that must be followed. In winter they consume one pair of leaves and produce a pristine new pair. From autumn when they finish flowering until spring when the old leaves are completely gone, Lithops require very little water in climates with warm sunny winters, and no water at all in cooler northern climates. Once those old leaves are completely dried up, they can be watered sufficiently to fully inflate the new leaves. Lithops will become dormant in very hot summer weather, and strange as it may seem, need less water in those hot conditions than when it is cooler. Their main growth spurt comes once the hottest part of summer is over and they can be given a few deep waterings at this time. Mature plants will produce a single yellow or white flower like an iridescent daisy which emerges from the centre of the fused leaves. Mature plants may also divide over the winter to produce double heads and eventually a large clump. In non-desert areas it is best to keep Lithops in a gritty free-draining soil that doesn't stay wet for too long because Lithops will burst or rot if they stay wet. One last requirement is lots of direct sun, Lithops will never be happy without several hours a day.
The copyright of the article Lithops in Plants & Bulbs is owned by Ian Nartowicz. Permission to republish Lithops in print or online must be granted by the author in writing.
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