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.

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.^[1] In 2014, Per Magnus Jørgensen proposed to use the name Gabura for what was then known as Collema fasciculare.^[2] The name was formally resurrected for use in 2020. Gabura has three species transferred from the genus Arctomia following molecular phylogenetic analysis.^[3]

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 lobes. 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 cortex—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 granules contain both partners of the lichen symbiosis and serve as ready-made propagules for dispersal.^[4]

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 discs 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 tholus) 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).^[4]

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.^[4]

Gabura lichens grow on bark (corticolous) or on soil (terricolous), and are often growing amongst moss.^[4]

• Gabura borbonica (Magain & Sérus.) Magain & Sérus. (2020)
• Gabura fascicularis (L.) P.M.Jørg. (2014)
• Gabura insignis (P.M.Jørg. & Tønsberg) Magain & Sérus. (2020)