The Paxillus involutus complex is studied with emphasis on European and Nor
th American species. Morphological and anatomical features are described an
d details of fruitbody anatomy (trama of cap, gills and stipe, hymenium of
gills and stipe), rhizomorphs, sclerotia, and cystidia of soil mycelia are
depicted in detail. Amplification of DNA with the Polymerase Chain Reaction
(PCR) is applied, and Restriction Fragment Length Polymorphisms (RFLP) are
analysed, too. The surface of spores is investigated by Scanning Electron
Microscopy (SEM). Comprehensive own observations and literature data are us
ed to discuss the ecology of Paxillus involutus s.l. which includes the new
European species Paxillus validus and P. obscurosporus as well as P. albid
ulus, P. involutus s.str., P. rubicundulus and P. vernalis. A detailed disc
ussion is included why the name P. rubicundulus should be used for the Euro
pean Paxillus species associated with Alnus. A synoptic table compares the
most important features of these six species.