Microsporum gypseum is a soil-associated dermatophyte that occasionally is known to colonise and infect the upper dead layers of the skin of mammals. The name refers to an asexual "form-taxon" that has been associated with four related biological species of fungi: the pathogenic taxa Arthroderma incurvatum, A. gypsea, A. fulva and the non-pathogenic saprotroph A. corniculata. More recent studies have restricted M. gypseum to two teleomorphic species A. gypseum and A. incurvatum. The conidial states of A. fulva and A. corniculata have been assigned to M. fulvum and M. boullardii. Because the anamorphic states of these fungi are so similar, they can be identified reliably only by mating. Two mating strains have been discovered, "+" and "–". The classification of this species has been based on the characteristically rough-walled, blunt, club-shaped, multicelled macroconidia. Synonyms include Achorion gypseum, Microsporum flavescens, M. scorteum, and M. xanthodes. There has been past nomenclatural confusion in the usage of the generic names Microsporum and Microsporon.
History
The teleomorphic states of this species were originally the first to be discovered by Arturo Nannizii for M. gypseum in 1927, but his contribution was largely ignored by the scientific community. Until Christine Dawson and J.C. Gentles discovered anamorph Arthroderma uncurvatum, the teleomorph of Trichophyton ajelloi. Shortly after this, D.M. Griffin rediscovered M. gypseum by Nanizzi, and another individual P.M. Stockdale also isolated the second teleomorph of the species naming it Nannizzia incurvatum. Stockdale then confirmed that Nannizzia incurvatum differed from the original isolate of M. gypseum isolated by Nannizzi and proposed that two teleomorphic states of M. gypseum exist for the anamorph, thereby naming the latter N. gypsea. Various authors, such as Stockdale, M.F. Visset, and J.W. Rippon have agreed that the differences in structure of the anamorphic state of the complex of M. gypseum are inadequate for making distinctions between anamorphic states because of how similar they look. It is now believed that very similar anamorphs, M. gypseum and M. fulvum, consist of three teleomorphs: N. gypsea, N. incurvatum, and N. fulva. Shortly after, Arthroderma replaced Nannizzia, where Arthroderma is depicting the teleomorphic states, and Microsporum refers to the anamorphic states.