Ainoa forms a thin, crust-like lichen body (
thallus) that adheres tightly to bare rock. In some specimens the surface breaks along stress lines (), producing minute flakes that can act as vegetative
propagules. A translucent of dead fungal cells coats the crust and gives it a slightly frost-like appearance, while any outer is absent. The internal
photosynthetic partner is a simple, spherical
green alga (a photobiont) that sits just beneath the surface; this arrangement means the lichen shows no orange tint when scratched, unlike species that harbour
Trentepohlia. Fertile structures are abundant and conspicuous. Each
apothecium (fruiting body) is a small, round 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 ) 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.
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. ==Ecology==