ASCOMYCOTA | LECANOROMYCETES > TELOSCHISTALES > Teloschistaceae

Genus Caloplaca, meaning 'beautiful patches'

Common name:            Firedot lichen

Synonym:                     Athalia holocarpa

Habitat:                          Coastal (for this entry, otherwise as text)

Substrata:                     Rock

Growth form:                Saxicolous

Thallus:                  Crustose

Apothecia:                    Lecideine

BLS identity rating:        Graded 1/5 (identification should be relatively straightforward)

Thallus thin, typically reduced or only partially developed, yellowish-grey (often considerably darker and almost blackish in some urban situations); apothecia relatively abundant, scattered or crowded; discs yellow-orange to dark orange with lighter margins, which are thick when young, but become very narrow or barely visible as the apothecia matures and the discs become convex.

It's regarded as an aggregate of several similar species so is usually treated as sensu lato (in the broadest sense); most often encountered on calcareous stone or concrete, but may also be found on other substrata, such as sandstone and other siliceous rocks or, very occasionally, on wood. On limestone, it is very likely Caloplaca (Flavoplaca) oasis, particularly if in association with Verrucaria species. This form has darker, more orange-brown than yellow-orange, apothecia.

The form found on the bark of trees generally has a more developed thallus and bright orange apothecia. I believe that in Britain the form is known as Caloplaca (Athallia) pyracea and is mainly recorded further north, particularly in Scotland. I surmise that this is the species I photographed in Austria, as described in the montane section under Athallia (Caloplaca) holocarpa.    

In theory, identification of the aggregate form is said to be easy (BLS - grade 1), but I'm not confident enough to say for certain that the small patch in the photograph featured here is correct. Spot testing may have helped, apothecia K + crimson, but that was something that I hadn't even considered at the time.