Athallia saxifragarum
Athallia saxifragarum is a species of terricolous crustose lichen in the family Teloschistaceae. First described by Josef Poelt in 1955 as a member of Caloplaca, it was reclassified into the genus Athallia in 2013 following molecular phylogenetics studies. This lichen is characterized by its thin white thallus and small yellowish-orange apothecia. It primarily grows on bryophytes and plant detritus, showing a particular affinity for Saxifraga species, and is typically found in calciferous or alkaline environments in Arctic and alpine regions, including Greenland, Svalbard, and the European Alps, with recent documentation in Fennoscandia. It also occurs in North America.
Taxonomy
It was formally described as a new species in 1955 by Josef Poelt, who classified it as a member of the genus Caloplaca. Ulf Arup, Patrik Frödén, and Ulrik Søchting transferred it to Athallia following a molecular phylogenetics-informed reorganization of the family Teloschistaceae.Description
Athallia saxifragarum is a lichen species characterized by its thin, irregularly shaped thallus that grows either within the substrate or on its surface, appearing white. Its apothecia are moderately abundant and somewhat clustered. These small, disc-shaped structures measure 0.2–0.7 mm in diameter and sit directly on the surface, slightly constricted at the base and pressed closely against the substrate. The apothecia are in form, meaning they have a rim containing algal cells. The central is flat and yellowish-orange in colour, occasionally developing a brownish tinge as it matures, with a surface that ranges from smooth to finely. The margin around the disc is not prominent or wavy and appears darker than the rest of the thallus, usually yellowish-orange like the disc or slightly paler, with a smooth texture.The internal structure includes an measuring 20–50 μm wide, with a poorly defined containing few algal cells. The is broad, composed of parallel hyphae, strongly glutinized, and colorless. The, which is the layer below the spore-producing layer, is 100 μm high, made up of unoriented to vertically aligned hyphae with mostly wide openings, and is colourless. The is also colourless. The hymenium, where spores are produced, is 70–80 μm high and colorless. The paraphyses have simple terminal cells that are swollen up to 6 μm wide and colorless, with subterminal cells up to 3 μm wide. The is distinct and yellow to yellowish-orange.
The asci measure approximately 50 by 17 μm. Each ascus typically contains 8 broadly ellipsoid ascospores that measure 10–12 by 6–7 μm, with a septum of about 5.5 μm.
Habitat and distribution
Athallia saxifragarum grows over bryophytes and accumulated plant detritus, often among Saxifraga species. In alpine Europe it has been reported from dead tufts of Saxifraga and from twigs of shrubs and other woody plants. In Arctic regions it is frequently recorded on Saxifraga oppositifolia and Dryas integrifolia, and appears confined to calciferous or otherwise alkaline sites, in dry habitats that are open to partly shaded.The species resembles Athallia pyracea but differs in ecology and spores: A. saxifragarum is mainly associated with plant detritus, whereas A. pyracea is more typical of woody substrates, and A. saxifragarum has a slightly larger spore septum.
Athallia saxifragarum is known from Arctic and alpine regions, including Greenland, Svalbard and the European Alps. It was reported as new to Finland and Norway in 2014 and to Sweden in 2023, and it also occurs in North America. Sequenced material has been reported from alpine localities in the Pirin Mountains, the Prokletije Mountains and the Retezat Mountains.