Lirellae

Lirellae are elongated, slit-like apothecia found in certain crustose lichens, most prominently in the family Graphidaceae. The term lirellate describes their narrow, finger- or scroll-like shape, which is often embedded in the thallus and may appear as a series of connected lines. Each lirellum houses the hymenial surface with asci that produce ascospores, which are released through a slit or narrow opening along the length of the structure when mature.

Morphologically, lirellae vary from simple, straight to curved or branched forms, and their coloration ranges from pale to dark, commonly contrasting with the surrounding thallus. They are typically attached to the substrate by a small base and can be continuous with the thallus or slightly raised. The internal anatomy and surface features of lirellae, along with spore characteristics and chemical composition, are important for species-level identification within Graphidaceae.

Ecologically, lirellate lichens are often corticolous, growing on tree bark in forested or shaded habitats, and are particularly prevalent in moist, tropical to subtropical regions, though they also occur in temperate zones. Their conspicuous, elongated fruiting bodies can aid field identification, but accurate species identification usually requires microscopic examination of asci and ascospores and sometimes chemical spot tests or thin-layer chromatography.

In taxonomy, lirellae are not a formal taxonomic group themselves but a morphological type of ascoma. They serve as a key feature in classification within Graphidaceae and related lichen groups, helping distinguish genera and species that produce lirellate apothecia from those with other apothecial forms.