Dimorphic fungi are fungi that can reproduce as either a mycelial or a yeast-like state. Generally the mycelial saprotrophic form grows at 25° C, and the yeast-like pathogenic form at 37° C. This dimorphism is important in the identification of mycoses, as it makes rapid identification of many pathogenic organisms possible.
Some diseases caused by dimorphic fungi are:
References
Thermally dimorphic fungus Wikipedia(Text) CC BY-SA