Bryobilimbia austrosaxicola

The lichen spreads over surfaces up to 5 cm across, forming a patchwork of pale grey, thin, angular areoles that are flat to slightly convex, each measuring between 0.2 and 0.3 mm. The core of the lichen, or medulla, does not produce a reaction with iodine. It has a primary photobiont of chlorococcoid nature, with cells measuring 5–9 μm in diameter, and a secondary photobiont that consists of small clumps of cyanobacteria, including both Stigonema, characterised by short, branched, yellow-brown filaments, and Gloeocapsa, noticeable for its groups of 2–4 cells within a reddish sheath.^[1]

Apothecia (fruiting bodies) are common, black, and range from flat to convex, with a diameter of 1.0–1.5 mm. They are generally circular but can become angular when confluent. The hymenium, a tissue layer containing the spore-producing asci, is infused with a red-brown pigment, and paraphyses (filamentous structures among the asci) are sparse and simple. The asci themselves are cylindrical to clavate, housing hyaline (clear), 1-septate ascospores measuring 10–12 by 3.5–4.0 μm.^[1]

Chemical analyses have not detected any secondary substances through thin-layer chromatography (TLC), and all standard chemical spot test reactions are negative.^[1]

This lichen's presence is only verified from three collections on Campbell Island, New Zealand, suggesting its rarity and specific habitat preference on mountainous sites. It tends to associate with a limited number of other species, including Placopsis sp. and Steinera radiata subsp. aucklandica.^[1] In the 2018 edition of the Conservation status of New Zealand indigenous lichens and lichenicolous fungi, Bryobilimbia austrosaxicola appears for the first time, where it is given the status "island endemic".^[3]