Black bread mold

Rhizopus stolonifer (black bread mold) is a widely distributed Mucoralean mold.

Asexual spores are formed within sporangia, which break to release the spores when mature. Germination of these spores forms the haploid hyphae of a new mycelium. R. stolonifer grows rapidly at temperatures between 15 and 30 degrees C.

Rhizopus stolonifer is a heterothallic species (Schipper 1984), in that sexual reproduction occurs only when opposite mating types (designated + and -) come in contact. Successful mating results in the formation of durable zygospores at the point of contact. Subsequently, the zygospore germinates and forms a sporangiophore whose sporangium contains both + and - haploid spores.

There are two varieties: R. stolonifer var. stolonifer produces straight, erect sporangiophores, whereas those of R. stolonifer var. lyococcos are curved. A closely related species, Rhizopus sexualis, differs primarily in being homothallic (self-compatible).

Distribution and Habitat
Rhizopus stolonifer has a pandemic distribution. It is capable of causing opportunistic infections of humans (zygomycosis). It is most commonly found growing on bread and soft fruits such as strawberries and peaches. Because its spores are common in the air, it can be grown within a few days by keeping moistened pieces of bread in an enclosed, humid environment.