Athallia holocarpa (Hoffm.) Arup, Fröden & Sochting  

=Caloplaca holocarpa (Ach.) A. E. Wade                 

   Thallus crustose, sometimes a little submerged, thin, areolate and cracked but most often reduced or partially developed and only around the apothecia, yellowish-gray, dirty-orange-gray, no prothallus or soredia. Apothecia usually numerous, most often in groups and more or less tight, 0.3-0.7 mm in diameter, disc flat to a little convex at the end, yellow, yellow-orange, bright orange (mountain forms), margin only in youth then barely visible or absent at the end, concolorous. Spores from asci with 8 spores, colorless, elliptical, polarilocular, 10-13 x 5.5-7.5 µm with a large septum of 3.6-5.4 µm, septum / spore ratio of 0.31- 0.45. Apothecia: K + purple. Not rare species, even in town, coming on the siliceous stones of old dirty and dusty walls, also on siliceous rocks, mortar, concrete, rarer on the bark of deciduous trees in general towards the dirty base of the trunk.

   Here we take this species in the strict sense according to: ARUP Ulf. "The Caloplaca holocarpa group in the Nordic contries, except Iceland" The Lichenologist. 41 (2): 111-130 (2009) based on a study of molecular biology. In this group it will be necessary to separate this species from the other species of this group characterized in particular by spores with a very large septum:

Caloplaca oasis  with orange-brown apothecia that grows on limestone or concrete nearby or on Verrucaria sp.

Caloplaca vitellinula (Nyl.) H. Olivier is a still difficult to interpret species that occurs on vertical walls of siliceous rocks or under overhangs and has a yellowish-gray rimmed and cracked thallus and scattered yellow to orange apothecia.

Caloplaca pyracea (Ach.) Th. Fr. with a well developed thallus and bright orange apothecia, growing on the bark of trees.