We describe the yeast genus Tortispora gen. nov., an early-diverging lineage in the Saccharomycetales that displays the formation of helical ascospores. The genus is based on 16 strains resembling Candida caseinolytica that were isolated from necrotic plant tissue in warm regions of the New World. Based on sequences of the D1/D2 domains of the nuclear large subunit rRNA gene, as well as other data, the strains are assigned to eight distinct species. The species are nutritionally specialized and share the unusual ability to hydrolyse casein and to grow on 1-butanol as sole carbon source. One species of the proposed new genus produces a simple ascus with a helical ascospore, whereas other species of the clade have failed to form ascospores. All species in the clade, including C. caseinolytica, are assigned to Tortispora gen. nov. The new binomials are Tortispora ganteri sp. nov., type species of the genus (SUB 86-469.5(T) = CBS 12581(T) = NRRL Y-17035(T)), Tortispora caseinolytica f.a., comb. nov. (UCD-FST 83-438.3(T) = CBS 7781(T) = NRRL Y-17796(T)), Tortispora mauiana f.a., sp. nov. (UWOPS 87-2430.3(T) = CBS 12803(T) = NRRL Y-48832(T)), Tortispora agaves f.a., sp. nov. (UWOPS 94-257.6(T) = CBS 12794(T) = NRRL Y-63662(T)), Tortispora sangerardonensis f.a., sp. nov. (UWOPS 00-157.1(T) = CBS 12795(T) = NRRL Y-63663(T)), Tortispora cuajiniquilana f.a., sp. nov. (UWOPS 99-344.4(T) = CBS 12796(T) = NRRL Y-63664(T)), Tortispora starmeri f.a., sp. nov. (G 91-702.5(T) = CBS 12793(T) = NRRL Y-63665(T)) and Tortispora phaffii f.a., sp. nov. (UWOPS 91-445.1(T) = CBS 12804(T) = NRRL Y-48833(T)). In addition, species formerly assigned to the genus Ascobotryozyma are reassigned to the genus Botryozyma. The genera Trigonopsis, Botryozyma and Tortispora are assigned to the family Trigonopsidaceae fam. nov.