Agaricus subrufescens Peck was cultivated first in the late 1800s in eastern North America. The type consists partly of cultivated material and partly of field-collected specimens. Once a popular market mushroom, the species faded from commerce in the early 20th century. More recently, a mushroom species growing wild in Brazil has been introduced into cultivation in Brazil, Japan and elsewhere. This Brazilian mushroom has been referred to by various names, most commonly as A. blazei Murrill (sensu Heinemann) and most recently as A. brasiliensis Wasser et al. The author first cultivated A. subrufescens in 1981 and has grown and studied Brazilian isolates since 1992. The species has an amphithallic pattern of reproduction. Based on DNA sequence analysis of the rDNA ITS region and on mating studies and genetic analysis of hybrid progeny, there is a strong case for conspecificity of the Brazilian mushrooms with A. subrufescens. Based on a study of the type and other data, the recent lectotypification of A. subrufescens is accepted. Data are presented on mushrooms of diverse geographical origins, including A. rufotegulis Nauta from western Europe, another apparent conspecific. A possible role for interpopulational hybridization in current populations of A. subrufescens is proposed. The agronomic history of the species is reviewed.