Leaf carbon stable isotopic composition data for 1002 orchid species representing 61% of the total number of orchid species described for Panama and Costa Rica were obtained from herbarium specimens to survey the occurrence of crassulacean acid metabolism (CAM). Carbon isotopic composition of leaf material showed a bimodal distribution with modes at -28 parts per thousand, indicating C-3 photosynthesis, and at -15 parts per thousand, indicating pronounced CAM photosynthesis. Strong CAM was present in 9.5% of species and in 31 of 162 genera studied. Twelve of these genera were not previously known to contain species exhibiting CAM. A checklist of orchids of Panama and Costa Rica with their delta 13C values and an updated list of all known orchid genera that possess species with the ability to perform CAM are presented. (C) 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163, 194-222.
