Orostachys Fischer (1809)
The genus Orostachys includes 13 species of small rosetted succulents from Russia, Pakistan, Kazakhstan, Mongolia, China, Korea and Japan, variously included under Sedum and Cotyledon. Some species have more succulent leaves than others. Each leaf carries a terminal spine. Plants are monocarpic but may persist by propagating themselves via stolons. Hundreds of pink or white bell-shaped flowers are carried on dense pyrimidal spikes.
Orostachys spinosa Meyer ex Berger 1930
is a cold-tolerant alpine from Siberia and Mongolia, with fleshy leaves arranged in a spiral according to the Fibonacci sequence. The mature rosette may be 4 inches in diameter after several years. It must be kept dry during winter dormancy and otherwise watered sparingly, avoiding getting water on the rosette. Bright light or diffuse sunlight helps to keep the rosette compact.
As with other Crassulaceae Orostachys spinosa employs Crassulacean Acid Metabolism (CAM) and is thought to be the most cold-tolerant CAM plant known. The relatively high sugar content of the leaves, compared with starch, may help it to survive extreme freezing temperatures to -40°C and even carry out photosynthesis under snow cover in its habitat.