AbstractThe rDNAs of strains of the cactophilicPichiaspeciesP. amethionina, P. antillensis, P. barkeri, P. cactophila, P. caribaea, P. deserticola, P. heedii, P. kluyveri, P. norvegensis, P. opuntiae, P. pseudocactophila, P. thermotoleransand their varieties and anamorphs were mapped with 15 restriction endonucleases, and compared toP. membranaefaciensandP. salictariaas possible non‐cactophilic relatives. The existence of species complexes among those taxa was confirmed.P. membranaefacienswas a plausible ancestral species, and its closest relative in the cactophilic group wasP. deserticola. These two species appeared to be moderately related toP. heediiand toP. barkeri, but the latter was shown clearly to belong to theP. kluyvericomplex, in spite of a 6 mol G+C difference in their nuclear DNAs.P. cactophilaandP. pseudocactophilaostensibly emerged fromP. norvegensis, a facultatively cactophilic yeast. TheP. amethionina, P. cactophilaandP. opuntiaespecies complexes appeared independent from one another and from all other species studied.P. salictariadid not appear to be related toP. amethionin
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