| TAXON: | Xanthoria calcicola Oxner (1937) |
| RECENT SYNONYMS: | – |
| FAMILY: | Teloschistaceae |
| GROWTH FORM: | Foliose, heteromerous |
| SUBSTRATES: | Calcareous, nutrient-enriched rock and hard artificial substrates such as concrete, cement, etc |
| PHOTOBIONT: | Trebouxioid alga |
| REPRODUCTION: | Isidia; apothecia, pycnidia occasional |
| ASCUS: | If present, clavate; apex Teloschistes-type; 8 spores |
| SPORES: | Ascospores if present ellipsoidal, polarilocular, 10-12.5(-15) × 7.5-9(-10) µm; conidia if present ellipsoidal to bacilliform |
| NOTABLE FEATURES: | Thallus deep orange, often orbicular; lobes wide, spreading, often pleated and overlapping; underside paler, attached to substrate by hapters not rhizines; isidia coarse, with ‘chunky’ or ‘knobbly’ wart-like appearance, usually abundant, crowded and often obscuring thallus centre; apothecia if present lecanorine, slightly stalked; discs orange |
| CHEMICAL TESTS: | Thallus K+ crimson-purple, UV+ red (parietin, minor amounts of other anthraquinones) |
| HABITAT: | Lowlands wherever suitable substrate available; nitrophilic |
| DISTRIBUTION: | Common in east, central and northern England; local in southwest England, Wales, Scotland |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Phacothecium varium, Sphaerellothecium parietinarium, Telogalla olivieri |
| IDENTIFICATION DIFFICULTY: | Green 1: Field identification possible |
| CONFUSION SPECIES: | Xanthoria parietina |
FIELD NOTES
Xanthoria calcicola is one of three Xanthoria species in Britain. It’s not as widespread as its ubiquitous cousin X. parietina. But it’s just as common in much of England, and it’s locally common elsewhere. And whereas X. parietina seems able to colonise just about any nitrogen-enriched substrate, X. calcicola prefers calcareous or nitrogen-enriched rock or hard artificial substrates, such as limestone, concrete, cement, mortar-washed brick and the like.
With its almost uniformly deep-orange thallus, and its foliose, spreading habit, X. calcicola is difficult to confuse with any other lichen. You might mistake it at very first glance with X. parietina, and extremely young thalli of the two species might look similar. But they’re otherwise easily distinguished:
- X. calcicola is isidiate, whereas X. parietina lacks any vegetative propagules. In some cases when X. parietina is damaged, its small regenerating lobules can appear a bit like knobbly isidia, but you’d be able to tell the difference upon closer examination.
- X. calcicola tends to lack apothecia, whereas X. parietina typically has very many. Even when X. calcicola develops apothecia, it also remains isidiate.
- The thallus of X. calcicola, as well as any apothecia if present, tend to be deep orange in colour. The thallus of X. parietina is more yellow in tone, with contrasting orange apothecia.
Indeed, apart from the superficial resemblance with X. parietina, X. calcicola is one of the most recognisable British lichens. See the specimen galleries below for a photo of both species side-by-side.
LAB NOTES
Xanthoria calcicola can normally be identified without microscopy.
SPECIMENS
Xanthoria calcicola : England : VC28 West Norfolk : TF9528 : October 2024 : On concrete bridge parapet
Xanthoria calcicola : England : VC14 East Sussex : TQ9418 : July 2024 : On calcareous cobble
Xanthoria calcicola : England : VC25 East Suffolk : TM3381 : March 2023 : On concrete fence post
