Placynthium glaciale is a species of saxicolous (rock-dwelling) crustose lichen in the family Placynthiaceae. It was described as a new species in 2020 by lichenologists Alan Fryday and Toby Spribille.
Taxonomy
The type specimen was collected in the Hoonah–Angoon Census Area of Glacier Bay National Park and Preserve, Alaska, on the upper end of Muir Inlet, where the lichen was found growing on an argillite-like boulder and exposed cobbles in post-glacial soil. The specific epithet glaciale alludes to its association with glacial forelands.
Description
Placynthium glaciale forms a thin, crust-like thallus that clings tightly to its substrate. A single patch is rarely wider than about 3.5 cm and averages 0.2 mm in thickness. The surface is olive-brown and densely studded with minute, cactus-like lobes (30–150 micrometers across). The photosynthetic partner is an unidentified cyanobacterium.
The spore-bearing bodies (apothecia) are scattered over the surface as round discs 0.3–0.8 mm in diameter, with dark brown to jet black centers and a persistent shiny black rim. The ascospores are often nearly square in outline, averaging 8.4–10.8 × 6.4–7.1 micrometers, and are unusually blocky and multi-partitioned. No asexual reproductive structures have been observed, and standard chemical spot tests yield no color reactions; thin-layer chromatography likewise detects no secondary metabolites.
Habitat and distribution
The species is only known to occur in Alaska, where it has been documented from Glacier Bay National Park, Petersburg Borough, Patterson Glacier, and Muir Glacier. It is one of ten Placynthium species found in Alaska. The lichen colonizes recently deglaciated rocks, consistent with its name referencing glacial environments.
