Caloplaca squamuloisidiata

Caloplaca squamuloisidiata is a species of saxicolous crustose lichen in the family Teloschistaceae. Described as a new species in 2006, it is found in southwestern and northern Europe.

Taxonomy

The species was formally described as new to science in 2006 by the lichenologists Pieter van den Boom and Víctor Rico. Its specific epithet squamuloisidiata refers to two of its distinctive features: the thallus and the presence of isidia. The species belongs to the genus Caloplaca, a large group of mostly orange or yellow lichens, though C. squamuloisidiata itself is pale green to grey with olivaceous patches. C. squamuloisidiata has a morphology that broadly aligns with that of the Caloplaca cerina group, although it does not belong in the Caloplaca cerina clade.
It is morphologically similar to Caloplaca chlorina but can be distinguished by several features, including its true isidia, arrangement of hyphae, and slightly larger conidia.

Description

Caloplaca squamuloisidiata has a distinctive crustose thallus that is - to -, often with a defined outline. The thallus appears pale green to greyish or pale grey with dark olivaceous patches. Its margins feature small that frequently develop into isidia—vegetative reproductive structures that are cylindrical to flattened, simple to branched or. The upper cortex is well-developed and, while a thin, usually visible appears white to brown around the thallus.
The reproductive structures include rare apothecia measuring 0.2–0.8 mm in diameter with pale to dark orange. The rim matches the thallus colour and can be smooth to somewhat or isidiate. Microscopically, the species has colourless, ascospores measuring 10–13 by 5–8 μm and produces simple, rod-shaped conidia from inconspicuous pycnidia immersed in the thallus. When tested chemically, the thallus shows no reaction to standard chemical spot tests, though pigmented parts turn purplish with potassium hydroxide solution.

Habitat and distribution

Caloplaca squamuloisidiata is known from four localities in the Iberian Peninsula: two in Portugal and two in Spain. It grows on acidic rocks, including quartzite, granite, and sandstone, in inland areas at elevations from 200 to 1,000 metres. In 2021, it was reported from the Gaupne area of Sogn og Fjordane, Norway, a biodiversity hotpot for lichens.
The species prefers shaded and sheltered rock faces, which are often slightly overhung and exposed to the north. It occurs in various vegetation zones of the Mediterranean region, from the thermomediterranean belt to the mesomediterranean and supramediterranean belts. The lichen is often found growing with other species such as Acarospora epithallina, A. hilaris, Caloplaca demissa, Ochrolechia androgyna, Ramalina pollinaria, Rinodina confragosa, Solenopsora vulturiensis, and various others, depending on the locality.