Arrhizus

Arrhizus is a genus name historically used for certain filamentous fungi in the family Mucoraceae, most often in reference to the sexual (teleomorphic) form of species now generally classed in the genus Rhizopus. In modern taxonomy, Rhizopus is the accepted name for the group, and Arrhizus arrhizus is typically treated as a synonym of Rhizopus oryzae. Consequently, Arrhizus is largely of historical or literature-specific interest, with some older sources still employing the Arrhizus designation to denote the sexual state of Rhizopus species.

Morphology and life cycle are characteristic of mucoralean fungi. Arrhizus/Rhizopus species form rapid–growing, threadlike, coenocytic hyphae. They produce sporangia on stalked sporangiophores, bearing sporangiospores that are dispersed asexually. When hyphae from compatible strains encounter each other, zygospores develop within zygosporangia as part of the sexual cycle.

Ecology and distribution are broad. These fungi are common saprotrophs found on decaying plant material, fruits, bread, and in soil. They can thrive in warm, moist environments and are frequently encountered in indoor settings where bread or fruit spoilage occurs.

Economic and medical relevance is notable. Some Rhizopus/Arrhizus species are important in food fermentation and biotechnology, while others are opportunistic pathogens that can cause mucormycosis in humans, particularly in individuals with weakened immune systems. Their spoilage activity also poses challenges in food safety and storage.

In summary, Arrhizus refers to a historic or alternate naming for the sexual form of certain Rhizopus fungi, with Rhizopus arrhizus (synonymous with Rhizopus oryzae) being the best-known example.