Ainoa

Ainoa forms a thin, crust-like lichen body (thallus) that adheres tightly to bare rock. In some specimens the surface breaks along stress lines (schizidia), producing minute flakes that can act as vegetative propagules. A translucent epinecral layer of dead fungal cells coats the crust and gives it a slightly frost-like appearance, while any outer prothallus is absent. The internal photosynthetic partner is a simple, spherical green alga (a chlorococcoid photobiont) that sits just beneath the surface; this arrangement means the lichen shows no orange tint when scratched, unlike species that harbour Trentepohlia.^[4]

Fertile structures are abundant and conspicuous. Each apothecium (fruiting body) is a small, round disc that sits directly on the thallus but narrows to a stalk-like base, giving it a button-on-a-pin profile. The disc itself is dark brown to almost black, flat to slightly cupped, and surrounded by a raised margin that persists for the life of the fruit body. Supporting this margin is a cup-shaped layer (the exciple) composed of long, thick-walled hyphae that darken with age. Above the exciple lies a clear spore-bearing layer (hymenium) 90–150 μm tall; it is threaded by slender, septate filaments (paraphyses) that branch sparingly and separate readily when mounted in water, a trait that helps distinguish the genus. The asci are cylindrical, hold eight ascospores, and have a faintly blue-staining apical dome typical of the Trapelia type. Spores are narrowly ellipsoidal, colourless, and lack both internal septa and the gelatinous sheath seen in many other crustose lichens.^[4]

Ainoa also produces asexual spores in tiny flask-shaped pycnidia embedded within wart-like swellings of the thallus. These pycnidia release very small, rod-shaped conidia. Chemically the genus is simple: the only consistently detected compound is gyrophoric acid, and even that is confined to the fruit bodies and pycnidia rather than permeating the entire crust.^[4]

All known species are saxicolous, preferring hard, siliceous rock in cool, often alpine environments where periodic wetting and drying favour lichens that can cling closely to their substrate.^[4]