Protoblastenia rupestris forme sur roche calcaire.

      This form differs from the type of Protoblastenia rupestris by its occurrence on limestone rocks. Its thallus is well developed and relatively thick, finely cracked, yellow-ochraceous. This form often cohabits with Verrucaria of the Verrucaria nigrescens group.

Watch out for Caloplaca flavovirescens whose thallus is also yellow but K+ purple and whose apothecia have a margin, also Athalia holocarpa and Flavoplaca oasis whose apothecia have a margin (at least initially) but whose thalli are often blackish.