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Xalocoa
Single-species lichen genus From Wikipedia, the free encyclopedia
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Xalocoa is a single-species fungal genus in the family Graphidaceae.[2] It contains the single species Xalocoa ocellata, a lichen. This bark-dwelling species forms thin grey-white crusts with unusually large, eye-like spots that can reach up to 4 millimetres across. It has a nearly worldwide distribution in areas with Mediterranean-type climates and was first scientifically described in 1831 based on specimens collected from France.
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Taxonomy
The genus Xalocoa was circumscribed in 2013 by the lichenologists Ekaphan Kraichak, Robert Lücking, and H. Thorsten Lumbsch. It contains Xalocoa ocellata,[3] a corticolous (bark-dwelling), crustose lichen that was originally described by Elias Magnus Fries in 1831 (as Parmelia ocellata).[4] The type specimen was collected from France.[3]
Xalocoa belongs to the subfamily Graphidoidae, and tribe Thelotremateae in the Graphidaceae. The genus is characterized by its greyish-white thallus covered by an epinecral layer, large apothecioid ascomata with exposed discs and thick, entire thalline margins, as well as a thin, reduced, uncarbonised proper exciple that lacks lateral paraphyses. The genus features a non-inspersed hymenium, pale brown, non-amyloid ascospores, bacilliform conidia, and contains the norstictic acid chemosyndrome. The genus name Xalocoa originates from the Catalan term xaloc, which signifies the sirocco, a warm wind that comes from the Sahara and affects Mediterranean regions. The species epithet pays tribute to Xavier Llimona, a Catalan researcher known for his work on Mediterranean lichens and his contributions to the taxonomy of the genus Diploschistes.[3]
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Description
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Xalocoa ocellata forms a thin, grey-white crust (the thallus) that is covered by an epinecral layer – a delicate, often slightly powdery film of dead fungal cells that helps the surface shed water. Its reproductive bodies (apothecia) are unusually large for the family, reaching up to about 4 mm across. Each apothecium is lecanorine: the round, exposed disc sits in a thick rim of thallus-derived tissue (the thalline margin), so the fruiting bodies look like tiny greyish eye-spots set into the crust. Beneath the margin lies a very thin, uncarbonised proper exciple (the cup-shaped tissue that lines the disc), and the spore-bearing layer (hymenium) is clear rather than shot through with oil droplets (non-inspersed).[3]
Microscopically, the asci produce eight pale-brown, multi-chambered (muriform) ascospores that lack any starch reaction (non-amyloid). The spores measure roughly 25–45 μm long and 10–15 μm wide and are divided by both transverse and longitudinal partitions (septa), giving them a brick-like appearance. Asexual reproduction is by slender, rod-shaped (bacilliform) conidia. Chemical spot tests detect norstictic acid, a secondary metabolite that often gives the medulla a yellow to red reaction with potassium hydroxide solution (the K test). Together, the large lecanorine apothecia, absence of lateral paraphyses, muriform spores and norstictic-acid chemistry distinguish Xalocoa from superficially similar genera in the family Graphidaceae.[3]
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Habitat and distribution
Xalocoa ocellata has a nearly cosmopolitan distribution, occurring in areas with a Mediterranean climate.[3] It has been recorded from Yunnan and Sichuan provinces in China.[5]
References
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