Historically, genus delimitation is based on spore morphology. Three main agaricoid genera have been distinguished: Rhodocybe, with bumpy spores, Clitopilus, with spores showing longitudinal ribs, and Entoloma, with angular spores.
In addition, two gasteromycete genera have been described with spores similar to those of Entoloma, viz. Richoniella, and Rhodogaster.
A recent study performed by Delia Co-David and myself used three molecular markers in order to reconstruct the phylogeny and spore evolution of Entolomataceae. The full text of this study is available on the downloads page
The following conclusions could be made
(1) The Entolomataceae are indeed monophyletic and include also the gasteroid genera.
(2) Clitopilus is nested within Rhodocybe. This means that these two genera must be merged. SInce Clitopilus is the older name, all Rhodocybe need to be transferred into this genus.
(3) Entoloma can best be retained as one, large genus with a huge variation in fruitbody morphology including the gasteroid Richoniella, and Rhodogaster. Furthermore, the classical subdivisions such as Entoloma, Nolanea, Leptonia,and Inocephalus are polyphyletic. New subdivisions need to be defined within the genus Entoloma, which is now the focus of our research and will be published in 2010.
(4) Most likely the angular Entoloma spores, and longitudinally ribbed Clitopilus spores are derived from a rhodocyboid ancestor.
Spore evolution schematized after the phylogenetic tree to the right of this page. In this theory, facets evolved only once, leading to the Entolomatoid spore. Clitopiloid spores originate also from the rhodocyboid ancestor.