A molecular phylogeny for the subfamily Pitcairnioideae was inferred to examine the distribution of crassulacean acid metabolism in the subfamily. For this purpose, a neighbour-joining tree with p-distances was built using a MatK chloroplast gene data set. The phylogenetic results of our analysis confirmed the monophyletic condition of most genera examined: Brocchinia, Dyckia, Encholirium, Fosterella, Hechtia and Puya. A paraphyletic basal sequence showed Hechtia branching off from the basal node, followed by Brocchinia, Cottendorfia + Navia phelpsiae, and Puya. The remaining taxa were divided into two groups: (a) Deuterocohnia meziana, Dyckia, Encholirium; Fosterella; Deuterocohnia spp. + Pitcairnia heterophyla; (b) Pepinia, Pitcairnia spp. and Navia igneosicola. The basal placement of the CAM genera Hecthia indicates that CAM may be a ‘primitive condition’ in Pitcairnioideae and that C3 species may have lost the ability to induce CAM. In this molecular tree, CAM metabolism appeared scattered throughout the tree. Current knowledge, however, does not exclude the possibility that CAM arose only once and it has been switching on and off in various lineages. Further detailed studies on photosynthetic metabolisms and the phylogenetic distribution of characters will provide a better basis on which to evaluate photosynthetic origins. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 261–268.
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