Representatives of an undescribed, haploid, heterothallic yeast species, P. euphorbiae, were recovered from insect-infested specimens of Euphorbia ingens. The new species is another representative of the apparently related group of heterothallic species, comprising P. rhodanensis, P. wickerhamii, P. veronae, P. amylophila, P. mississippiensis and P. meyerae. While no mating response was observed in interspecific mixtures of the mating types of the new species with the mating types of the first 5 mentioned species, a sexual response, manifested by the formation of non-sporulating zygotes was nevertheless detected with the mating types of P. meyerae. Prototrophic hybrids obtained by crossing auxotrophic mutants of the mating types of P. euphorbiae and P. meyerae were only partial recombinants. A description of the new species is given.