Gabura

''Gabura'' is a small genus of lichen-forming fungi in the family Arctomiaceae. These lichens form low-growing patches that range from thin, crust-like films to small, crumpled cushions, appearing dark olive-green to almost black when dry but swelling like a sponge and becoming softer when wet. They partner with blue-green algae called ''Nostoc'' and grow on tree bark or soil, often among mosses, reproducing through tiny disc-shaped fruiting bodies that contain long, multi-celled ascospores.

Taxonomy

Although it was originally circumscribed in 1763 by French botanist Michel Adanson, the name was nomen rejiciendum–it was "suppressed" against the conserved name ''Collema'', and for a long time considered a synonym of '' Arctomia''. In 2014, Per Magnus Jørgensen proposed to use the name ''Gabura'' for what was then known as ''Collema fasciculare''. The name was formally resurrected for use in 2020. ''Gabura'' has three species transferred from the genus ''Arctomia'' following molecular phylogenetic analysis.

Description

''Gabura'' forms low-growing thalli that range from a thin, crust-like film firmly attached to the substrate to small, crumpled cushions whose margins break into indistinct . When dry the surface is a dark olive-green to almost black; in many species it absorbs water like a sponge, swelling noticeably and taking on a softer texture. A true —the protective outer skin seen in many lichens—is poorly developed or absent, so the underlying tissues show through. Some taxa produce powdery patches called soralia, whose yellow- to brown-tinged contain both partners of the lichen symbiosis and serve as ready-made propagules for dispersal.

Embedded among the fungal threads are clusters of the cyanobacterium ''Nostoc''; its orangey-green cells, measuring 5–7 micrometres across, sit within a clear jelly that helps the thallus retain moisture. Sexual reproduction, where it occurs, takes place in minute disc-shaped fruit bodies (apothecia) that arise directly from the lobes and remain almost stalkless. These lack a distinct rim of thallus tissue and may be flat or gently domed. Inside, slender branched filaments (paraphyses) stand amongst the asci; their tips broaden and darken to brown. Each ascus is of the '' Trapelia'' type: it has a thickened apex (the ) that remains colourless in iodine, while the surrounding gelatinous sheath stains blue, and it normally contains eight long, spindle-shaped ascospores divided by multiple cross-walls (septa).

Asexual reproduction is achieved through flask-shaped pycnidia sunk in the thallus; these release tiny, rod-shaped conidia. Chemical screening with thin-layer chromatography has so far revealed no secondary metabolites, making the genus unreactive with standard chemical spot test. The combination of a swelling, dark thallus with optional soralia, cyanobacterial photobiont, ''Trapelia''-type asci and multiseptate spores distinguishes ''Gabura'' from superficially similar gelatinous crusts in the same habitats.

Ecology

''Gabura'' lichens grow on bark (corticolous) or on soil (terricolous), and are often growing amongst moss.

Species

*'' Gabura borbonica''
*'' Gabura fascicularis''
*'' Gabura insignis''

References

{{Taxonbar, from=Q25407175

Baeomycetales
Baeomycetales genera
Lichen genera
Taxa described in 1763
Taxa named by Michel Adanson