Three classes of changes are indicated by the symbol separating the names:
-> Indicates a widely accepted name change. In these cases the name in the text is considered synonymous with the alternative and the alternative takes priority for some reason
(e.g. Aleuria rhenana -> Sowerbyella rhenana)<-> Indicates a debatable name change. In these cases the name in the text is considered synonymous with the alternative, but which names takes priority is debatable.
(e.g. Boletus chrysenteron <-> Xerocomus chrysenteron)<-R-> Indicates a regional change. In these cases both names are valid because they actually are different taxa that occur in different regions of the world. The name on the right is correct for the west coast of the United States.
(e.g. Amanita rubescens <-R-> Amanita novinupta)
Texts:
Mushrooms Demystified by David
Arora