“Common Name: Blewit”
Lepista nuda is a widely used synonym that should no longer be used since Lepista has been synonymized with Clitocybe (Harmaja 2003). However, as of June 2007 according to Index Fungorum both names are valid, so I’m leaving it that way on Mushroom Observer.
The primary issue here is a debate about the correct type for the genus Clitocybe. Some, including Singer, take the type to be C. gibba. However, the majority of experts now take C. nebularis to be the type. If you take C. nebularis to be the type then Lepista becomes a deprecated synonym of Clitocybe and Clitocybe nuda is the correct name for this species.
Clitocybe nuda is very similar to Clitocybe glaucocana. According to Denise Gregory’s key to Clitocybe in California (http://www.mykoweb.com/CAF/keys/Clitocybe_key.pdf), they can be distinguished based on the cap color when young. In the case of C. nuda they should be deep violet or purple. C. glaucocana, on the other hand, is light violaceous, light blue or faintly purple when young. It would be nice to know if there are other reliable ways to distinguish between the two species.
As a side note the type species for Lepista is L. panaeolus which from photos looks pretty similar to C. nuda. Singer separates Lepista from Clitocybe on the basis of the smoothness of the spores(!). I have heard that others separate them based on the spore color (pink for Lepista, white for Clitocybe). It’s worth noting that when used as the sole differentiation between genera, spore color and smoothness of spores have not been getting much support at the molecular level.