[4] The species was later transferred to its own genus by Amanda Xavier-Leite, Marcela Cáceres, and Robert Lücking in 2023 based on molecular phylogenetics analysis that showed it was unrelated to Calenia in the strict sense and instead allied with Asterothyrium.

Monocalenia is distinguished by its smooth thallus lacking setae, erumpent and zeorine apothecia with pruinose discs containing epithecial algae, and unusual single muriform ascospores.

While some morphologically similar species exist (like Calenia lueckingii), molecular evidence supports Monocalenia's placement as a separate genus based on its unique combination of characters and phylogenetic position.

While some other species in the family share individual features with Monocalenia, this particular combination of characteristics – especially the single-spored asci and presence of algal cells in the apothecia – sets it apart as a distinct genus.

It has also been recorded from the Galápagos Islands (Ecuador) on Isla Santa Cruz in the upper moist zone above Bella Vista at 600 m (2,000 ft) elevation, where it was found growing on Malcolmia leaves.