Clitopilus argentinus is reported for the first time from North America. A full description and illustrations of the basidiomata and microscopic structures are provided. An X-ray elemental analysis of the diagnostic ‘hyaline’ incrustations of the pileus surface shows these extracellular structures to be composed mainly of calcium and magnesium. In addition, a multispore culture of this collection produces basidiomata in vitro. Clitopilus incrustatus Singer and C. fuscogelatinosus Redhead & Baroni are also discussed.