ECOPHYSIOLOGY AND DISTRIBUTION OF THE ENDEMIC LEAFLESS SPURGE EUPHORBIA-APHYLLA AND THE INTRODUCED EUPHORBIA-TIRUCALLI (EUPHORBIACEAE, EUPHORBIA SECT TIRUCALLI) IN THE CANARY-ISLANDS

The leafless spurge Euphorbia aphylla (Euphorbiaceae), an endemic spec ies restricted to several of the Canary Islands where it inhabits coas tal and arid localities, expresses Crassulacean Acid Metabolism (CAM) when it is subjected to summer drought. A flexible CAM is consistent w ith the general ecology of the species. It is the only member of sect. Tirucalli native to the Canary Islands and is at the north-western ed ge of the section's biogeographical range. The other members of the se ction have a paleotropic distribution and are found throughout Africa. Many of them are regarded as obligate CAM plants, including E. tiruca lli which was used as a comparison in ecophysiological experiments exa mining the response of E. aphylla to drought and temperature.