[7] In recent decades, the once large genus Parmelia has been divided into a number of smaller genera according to thallus morphology and phylogenetic relatedness.

[3]: 78  The upper surface is pale bluish-gray to light brown in direct sunlight, with a network web-like ridges and depressions.

These include Arctoparmelia,[10] Bulbothrix, Canoparmelia, Cetrariastrum, Concamerella, Everniastrum, Flavoparmelia, Hypotrachyna, Neofuscelia, Paraparmelia, Parmelina, Parmotrema, Pseudoparmelia, Relicina, Relicinopsis, Xanthomaculina, and Xanthoparmelia.

For example, while pruina (a dusty looking surface appearance) was previously considered a diagnostic feature in isidiate Parmelia species,[12][13] studies have shown that individual specimens can vary in their degree of pruinosity.

[7] The incorporation of molecular methods in Parmelia taxonomy has led to the discovery of cryptic taxa, such as P. encryptata[18] and near-cryptic species like P. rojoi.

[20] Later authors have suggested, however, that this generic placement is not appropriate for the current concept of Parmelia, and that because of the dearth of specimens available for analysis, it is impossible to know for certain which of the many foliose genera in the family Parmeliaceae is best suited for these fossils.

The lower surface of the thallus is black (or close to it), and has rhizines (either simple or branched) that function as holdfasts to attach it to its substrate.

The study also found that the mode of reproduction (whether through soredia or isidia, two types of vegetative propagules) did not significantly affect the specificity of fungal-algal partnerships.

The Parmelia mycobiome includes core fungal members like Cutaneotrichosporon debeurmannianum and various Chaetothyriales and Dothideomycetes species, which persist across different locations.

These fungal communities appear to be highly adaptable, allowing Parmelia to maintain consistent mycobiome features across diverse environmental conditions.

Both Parmelia saxatilis and P. sulcata are considered species of least concern due to their widespread distribution, abundance, and stable populations.