M. inermis M. richardsonii Masonhalea is a genus of two species of lichenized fungi in the family Parmeliaceae.

[1] The genus was circumscribed by Swedish lichenologist Ingvar Kärnefelt in 1977, with Masonhalea richardsonii as the type, and at that time, only species.

[2] The unusual morphology of this species – a vagrant lichen – attracted interest from several lichenologists, resulting in its placement in several genera, including Cornicularia, Evernia, Everniopsis, Platysma and Parmelia.

[3] In 2017, Divakar and colleagues used a recently developed "temporal phylogenetic" approach to identify temporal bands for specific taxonomic ranks in the family Parmeliaceae, suggesting that groups of species that diverged within the time window of 29.45–32.55 million years ago represent genera.

[6] Both Masonhalea species feature lateral apothecia, pycnidia on the thallus margin, a layer of cortical tissue beneath the wall of the pycnidia, and bacillariform (short cylindrical) conidia.