Taxonomic clarification of Cladosporium trichoides Emmons and its subsequent synonyms

Abstract

Cladosporium trichoides Emmons has been treated by some mycologists as a synonym of Cladosporium bantianum (Sacc.) Borelli and has been transferred to the genus Xylohypha (Fr.) Mason. In the present study, a herbarium specimen of C. bantianum (Torula bantiana Sacc.) Borelli, prepared by Saccardo, was compared with a herbarium specimen and a living type culture of C. triochoides by light and scanning electron microscopy (SEM) and was found to be dissimilar. Herbarium specimens and living cultures of Xylohypha nigrescens, the type species of the genus Xylohypha, were also compared with those of C. trichoides and other pathogenic Cladosporium species. Fundamental differences were found between X. nigrescens and Cladosporium species, in colony morphology, manner of sporulation and conidial morphology. All Cladosporium isolates produced olive-black colonies regardless of environmental conditions, bore brown pigment on the walls of the vegetative hyphae as well as on the walls of the fruiting structures and produced branched chains of conidia either from well differentiated or poorly differentiated conidiophores, or directly from the hyphae. By SEM, conidia showed strong to moderately protruded hila, and the basal contour of the conidia was always truncated. On germination, hyphal tubes were produced randomly from the surface of the conidia. In contrast, X. nigrescens produced white colonies with or without brown centres, depending on the culture medium, bore pigment on the conidial walls and on conidiogenous cells but not on the vegetative hyphae and produced infrequently branched conidial chains, usually from intercalary conidiogenous cells which were globose to hat-shaped. Conidial hila were nonprotruding but, instead, were deeply concave and pore-like. The basal contour of the conidia was round and germ tubes were produced only from the pore-like hila. These results indicate that C. triochoides Emmons is different from C. bantianum (Sacc.) Borelli and that the reclassification of C. trichoides into the genus Xylohypha was not warranted.