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Cyst-forming coccidia of the genus Sarcocystis (Alveolata: Apicomplexa: Coccidea) parasitize vertebrates worldwide. Data from the small subunit rRNA genes (SSU) and the D2 domain of the large subunit rRNA genes were used to reconstruct phylogeny for all species in the Sarcocystidae for which sequences are currently available. We have focused on the evolutionary history of species that circulate between snakes as definitive hosts and rodents as intermediate hosts. Trees were reconstructed using maximum parsimony, minimum evolution, maximum likelihood and the bayesian phylogenetics. Our reconstructions support monophyly of Sarcocystidae but fail to robustly resolve the relationship within clades. Using a concatenated dataset of available rDNAs, the "isosporoid" coccidia Neospora, Toxoplasma, Besnoitia, Isospora and Hyaloklossia form a sister group to the monophyletic Sarcocystis. Moreover. we show that Sarcocystis from arboreal vipers of the genus Atheris, which are endemic to the mountain rain forests of the Equatorial Africa, are monophyletic, with sister species parasitizing the desert viper Pseudocerastes persicus from the Near East. We report the co-evolution of Sarcocystis spp. with their final snake hosts. The geological history of the African continent, mountain ranges, forests and general SSU rDNA rates were used to construct a linearized tree. Possible origin of the heteroxenous life cycle of Sarcocystis is discussed. (C) 2003 Elsevier Science (USA). All rights reserved.