ABSTRACTEvolutionary relationships ofLentinusto the Tricholomataceae and Polyporaceae were studied using restriction analysis of nuclear-encoded ribosomal RNA genes (rDNA). Five species ofLentinus, three species in the Polyporaceae and two species in the Tricholomataceae were examined. Ribosomal DNA phenotypes were determined by restriction endonuclease digestion of enzymatically amplified rDNA (PCR fingerprinting). This method generates restriction fragment length polymorphism data without Southern blotting or autoradiography. With five different four-base restriction enzymes, one hundred and one unique restriction fragments were resolved. Among the 16 individuals studied, there were twelve different rDNA types. A similarity matrix based on presence or absence of comigrating restriction fragments was analyzed with UPGMA, complete and single-linkage analysis (using the NTSYS computer package), and Fitch-Margoliash and KITSCH analysis (using the PHYLIP computer package). Results of all analytical approaches were highly consistent and strongly suggest thatLentinus tigrinusis more closely related to the Polyporaceae than to the Tricholomataceae. Morphological characters (dimitic hyphae and hyphal pegs) also support this hypothesis. The other species ofLentinusappear to be intermediate between the Polyporaceae and Tricholomataceae and could not be clearly assigned to either family. The results also suggest thatLentinusis paraphyletic and, therefore, that lamellae have arisen repeatedly by convergent evolution.