We have identified two nomenclatural problems in the genus Parmotrema.
The name Parmotrema incrassatum Hale was invalidly published since it
lacked both a Latin description and type designation, and Parmotrema
michauxianum (Zahlbr.) Hale is a synonym since there is an earlier epi
thet available for that species. We provide validation of the first sp
ecies and a new combination for the second to resolve these nomenclatu
ral issues.