What fungus is commonly known as black bread mold?

The fungus commonly known as black bread mold is Rhizopus stolonifer.

It is one of the molds that can appear rapidly on stale bread, especially when warmth and moisture allow its threadlike hyphae to spread. The dark appearance comes from mature sporangia, rounded structures that produce and release large numbers of spores. Before those structures darken, the growing mold may look white or gray and cottony.

Rhizopus stolonifer is a saprotroph: it obtains nutrients by breaking down organic material outside its body and absorbing the resulting compounds. It is cosmopolitan and can colonize many foods, as well as fruits and vegetables. The species can cause soft rot in produce and is also associated with post-harvest decay.

A frequent mix-up is treating every dark mold on bread as the same species. Several fungi can grow on stored food, but Rhizopus stolonifer is the traditional textbook answer for black bread mold. Its former scientific names, including Rhizopus nigricans and Mucor stolonifer, can also create confusion in older references.