[4] The genus Platismatia was historically classified within Cetraria by Erik Acharius in the early 1800s, along with several other superficially similar taxa that were later moved to other genera like Asahinea and Cetrelia.

A comprehensive molecular phylogenetic study published in 2023 examined relationships within Platismatia using both newly generated and existing internal transcribed spacer (ITS) sequence data.

The widespread P. glauca was found to contain two distinct, highly supported clades that showed no apparent morphological or geographic differences.

Additionally, the western North American endemics P. herrei and P. stenophylla were not recovered as reciprocally monophyletic, suggesting they may represent a case of recent speciation or possibly conspecific taxa requiring further investigation.

Species producing asexual propagules (either isidia or soredia) generally show larger geographic ranges than their sexually reproducing relatives, though exceptions exist.