Diagnosis. A saxicolous species with deep orange to ferruginous red apothecial discs lined by a thin, concolorous rim and a pale to deep olive thalline margin on an areolate to irregularly subsquamulose deep olive, sometimes abundantly isidiate thallus; clearly distinguished from Caloplaca sideritis, if the thalli produce isidia, but even specimens lacking vegetative propagules are phylogenetically distinct by their different ITS.
Type. Ecuador, Galápagos: San Cristóbal, SE-exposed slope of Cerro Tortuga, ~4.5 km inland from the NW-coast, 0°44′55″S, 89°23′33″W, 110 m alt., dry zone, open Piscidia carthagenensis woodland with few Bursera graveolens and dense understory of Croton scouleri, Cordia lutea, and Mentzelia aspera on rocky SE-exposed slope of hill, on rock, 25-Apr-2007, Bungartz, F. 6516 (CDS 34733‒holotype; GenBank Accession number nrITS: MT967427).
Description. Thallus areolate to irregularly subsquamulose, of discrete, ± convex, up to 0.4 mm broad areoles, effuse, with a blackish hypothallus between the areoles, but often confluent and not forming a distinct prothallus along the periphery; two morphotypes: (1) surface pale to deep olive, lacking isidia, smooth and ± shiny, areoles ± lined black along their edges, epruinose or irregularly covered in a faint, farinose, white pruina (2) surface completely obscured, densely isidiate, isidia granular, 60–80 μm in diam., pale to deep olive, ± dull, typically not shiny, epruinose or irregularly covered in a faint, farinose, white pruina. Apothecia sparse, sessile, 0.6–0.9 mm in diam., dispersed in between the isidia or isolated among non-isidiate areoles; ‘zeorine’ to almost biatorine, thalline margin dark olive to almost black, soon excluded by being pushed below, proper margin 50–60(–80) μm, increasingly prominent, regularly circular, darkened towards the outside, forming a deep orange rim inside, towards the disc, epruinose to coarsely whitish pruinose, C-, K-; disc concave to plane, deep orange to ferruginous red, darker than the margin; with indistinct pruina, C-, K+ purple; epihymenium with both pigment granules and diffuse pigmentation, the orange granules not extending into the outer exciple, C- (± orange red intensifying), K+ purple, the diffuse brownish black to violaceous pigmentation contiguous with the outer exciple, C+ yellowish brown, K-; proper exciple soon dominant, differentiated into an inner, hyaline part, lacking crystals, and an outer brownish black to deeply violaceous part, the pigmentation diffuse, lacking pigment granules, C+ yellowish brown, K-; thalline exciple initially developed along the outside, soon pushed below, excluded, the central part densely filled with trebouxioid photobionts and small crystals that dissolve in K, the outside brownish black to deeply violaceous and contiguous with the proper exciple, the pigmentation diffuse, lacking pigment granules, C+ yellowish brown, K-; subhymenium and hypothecium not differentiated, hyaline, not inspers; asci clavate, Teloschistes-type; ascospores 8/ascus, polaribilocular, broadly ellipsoid to almost globose, spore dimensions of the isidiate morphotype (8.6–)9.3–12.8(–15.2) × (5.6–)6.3–8.0(8.8) μm, with a thick, (2.4–)3.0–4.7(–7.3) μm wide septum (n = 48), spore dimensions of the non-isidiate morphotype (5.7–)8.8–12.1(–13.5) × (5.5–)6.3–8.4(–9.8) μm, with a thick, (2.3–)3.1–4.7(–5.5) μm wide septum (n = 40). Pycnidia unknown.
Chemistry. Thallus P-, K-, C-, KC-, UV- (dull), apothecia P-, K+ purple, C-, KC-, UV- (dull); no secondary metabolites detected in the thallus; apothecia with dominant proportion of parietin and smaller proportions of teloschistin, fallacinal, parietinic acid and emodin. This corresponds to chemosyndrome A sensu Søchting (1997), but additionally smaller proportions of chlorinated anthraquinones like fragilin, 7-chloroemodin and 5-chloroemodin have been detected in some specimens.
Etymology.Named for its superficial similarity to the North American C. sideritis.
Ecology and distribution.Known only from the Galapagos. Both morphotypes are saxicolous, the isidiate one is less common; generally found in shaded and ± sheltered as well as sunny, wind- and rain-exposed habitats, from the coastal zone throughout the dry into the lower transition zone.
Notes. The two different morphotypes were originally considered two different species (see list of excluded taxa below). Although there is some variation in ITS sequence data, the sequences form a well-supported clade and a separation of the two morphotypes as separate species is not supported.