Karyology and hyphal characters as taxonomic criteria in ascomycetous black yeasts and related fungi.

Mycelial development of seventy-three strains of black yeasts and related fungi were studied, and numbers of nuclei per hyphal cell were counted. Two main patterns were apparent in expanding hyphae, viz. (1) uninucleate expanding hyphal cells, septum formation strictly following mitosis, and (2) multinucleate, branched, aseptate hyphal tips, septa being formed in a later stage, leading to oligo- or uninucleate mature cells. Characteristic genera in the two groups are Exophiala and Aureobasidium, respectively. In Zasmidium and in some Ramichloridium species all mycelial cells are oligonucleate. The character is indicative for relationships at the family level in black yeasts.