Found in South Africa, it was formally described as a new species in 2021 by John Alan Elix, Helmut Mayrhofer, and Wolfgang Wetschnig.

The type specimen was collected in the Knersvlakte (Namaqualand, northern Cape Province), at an altitude of 150 m (490 ft).

The species epithet refers to its subeffigurate marginal lobes (i.e., more or less irregular or without form).

The results of standard chemical spot tests are: thallus K+ (yellow), P+ (yellow-orange), and C−.

Buellia subeffigurata contains thiophanic acid as a major secondary chemical, and isoarthothelin and atranorin as minor compounds.