干旱区生态环境知识资源中心

Environmental hypotheses accounting for the distribution of succulents are many and varied and include the notion that this leaf type is more common in regions of low but predictable rainfall and saline areas but is absent or rare in regions with regular frosts. This paper tests the low temperature control of distribution hypothesis on all 5 varieties of the widely distributed succulent Cotyledon orbiculata in southern Africa to determine whether it has morphological and physiological attributes which confer tolerance to low temperatures. The low temperature survival limits (-6.1 to -10.4-degrees-C) of this species are very similar to those determined for other desert succulents on other continents. In addition, the current geographical range of C. orbiculata cannot be predicted from the temperature tolerances of even the most resistant organs examined in this study and no special modifications could be found to explain the occurrence of this species in regions with regular frosts (up to 90 nights per year). The results of the study caution against making predictions concerning the distribution of succulents in relation to past and future climate changes without more experimental evidence.