Masters of camouflage, living stones often grow unnoticed on rocks or sand. Their low profile lets them withstand drying winds and go unseen by herbivores. These plants tolerate extreme temperatures of up to 50oC by day, dropping to near freezing at night.
Living stones belong to the Aizoaceae family, made up of 100 genera native to the deserts of South Africa. They belong to the genus Lithops (from the Greek word lithos, stone) and are recognizable by their two fleshy leaves separated by a slit from which flowers and new leaves emerge. They bloom briefly, abandoning their camouflage just long enough to attract pollinators.
During dormancy, Lithops need no water. The leaves shrink, and the plant retracts to ground level. This is an excellent means of defense against drying winds, the blazing sun, and herbivores. This dormant season can last for up to six months.
These plants had their heyday back in the times of the dinosaurs, some 150 million years ago. Although the cycads resemble palm trees, they are actually related to conifers, in that they produce cones where the sexual cells form. The plants are either male or female, so it takes one plant of each sex to produce viable seeds.
Most cycad species have very restricted geographic distributions. This is a problem for their survival and many cycads are on the Red List of endangered species (IUCN). Loss of habitat and their popularity with collectors have caused their populations to decline.
Cycads comprise three plant families and include the genera Cycas, Zamia, Encephalartos and Dioon, all of which can be seen in the Hacienda and Arid Regions Greenhouse.
The epiphytic cacti, native to moist tropical forests, often grow high up in trees, clinging to them for support without actually feeding on them.
Not much sunlight penetrates through the canopy, so the stems of these cacti are generally flattened or cylindrical, to capture as much light as possible. Since there are fewer herbivores this high up, their spines are smaller. They produce colourful, fleshy fruit, to attract birds and help spread their seeds.
The more cultivated epiphytic cactus is probably the Christmas cactus (Schlumbergera), a horticultural hybrid for which there are many cultivars.