Aulaxina comprises thin,
crustose lichens that grow on the surface of living leaves in humid tropical forests. The
thallus forms small, greyish to whitish patches on a delicate, algae-free . From this arise minute, erect, black thallus hairs, typically up to about 0.2 mm high, which are sterile and lack algal cells. The is a unicellular, green alga arranged in a single within the thallus. The fruiting bodies (
apothecia) are blackish and variable in outline, ranging from rounded or angular to elongate, and sometimes forked, and can resemble the lirellae of some species in the
Opegraphaceae or
Graphidaceae. In young apothecia the dark lateral completely covers the , which later opens in a star-like or slit-like fashion to expose the
hymenial surface. The apothecia are usually with a somewhat constricted base. In vertical section, the lateral exciple is dark brown to black and often , while the hymenium is non-
amyloid and traversed by numerous slender
paraphyses that are richly branched and
anastomosing – that is, forming an interconnected network. The
asci each contain one or a few colourless, thin-walled
ascospores that are transversely
septate to (divided by internal cross-walls), enclosed in a gelatinous outer layer that can make their edges appear indistinct when viewed in water mounts. Species of
Aulaxina also produce dark ,
asexual reproductive structures that occur among the thallus hairs. These consist of very small, rod- to club-shaped black stalks, straight or slightly curved, arising mainly from the prothallus and terminating in a small head of densely packed, hyaline
hyphae. When moistened, the outer hyphae swell and separate into chains or short segments that function as
diaspores of the fungal partner. Differences in the form of the hyphophores and their propagules are useful for distinguishing species within the genus. ==Species==