Sexual reproduction be either homothallic or heterothallic. The second type is self-fertilization or selfing (in homothallic fungi). In homothallic species, sexual structures occur in single culture. Both heterothallic and homothallic strains of Dictostelium can undergo mating. Both varieties are self-fertile (homothallic), which means that a single strain can mate with itself. "Phytophthora cinnamomi" is also capable of self-fertilization (i.e. it can be homothallic). Homothallic "D. discoideum" strains AC4 and ZA3A are also able to produce macrocysts. "F. graminearum" is a haploid homothallic ascomycete. This contrasts with homothallic strains that appear to express both mating types. The ascomycete fungus "Pneumocystis jirovecii" is considered to be primarily homothallic. It is a homothallic, self-fertile organism. "A. nidulans", a homothallic fungus, is capable of self-fertilization. In "D. mucoroides" (DM7) homothallic mating, cells are directed towards sexual development by ethylene. "C. cymbopogonis" is homothallic. Homothallic reproduction is characterized by the fusion of the asexual oogonium and antheridium.