Are orchids C3, C4, or CAM plants?

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Katia Silvera (Univ. of Nevada) is studying the phylogenetic distribution of CAM in orchids. She has found that it has evolved repeatedly in different orchid lineages, and is most common in orchids from hot, low-elevation habitats. Here's a link to one of her papers: Crassulacean Acid Metabolism and Epiphytism Linked to Adaptive Radiations in the Orchidaceae -- Silvera et al. 149 (4): 1838 -- PLANT PHYSIOLOGY