Description
Arthrorhaphis species either have no thallus of their own or form a thin crust that lacks a distinct marginal zone. When the fungus grows independently it soon breaks into tiny, strongly convex scales ( squamules ) that are bright greenish yellow to whitish grey; these scales have no true protective cortex , only a delicate colourless surface layer. Some taxa also produce fine, powdery soredia that serve as propagules for vegetative reproduction. The photobiont partner is a chlorococcoid green alga that forms a conspicuous, compact layer of cells. [5]
The sexual fruiting bodies (apothecia) sit directly on the thallus or nestle between the squamules. They are black and either urn-shaped ( urceolate ) or disc -like, and many are packed with crumbly, brown-green granules that resemble droplets. The surrounding wall ( exciple ) is poorly developed, consisting of loosely woven hyphae with markedly swollen walls. Threads called paraphyses weave through the spore-bearing layer (hymenium); they are slender, freely branched and interconnected, with only slight thickening at their tips. Oil droplets are often scattered throughout the hymenium. [5]
Each ascus contains eight ascospores and is club-shaped ( clavate ); the apex shows only minimal thickening and reacts negatively to iodine (K/I–) but does have a small transparent ocular chamber . The spores are long and narrow—ranging from cylindrical to nearly needle-like—and are divided by three to fifteen, occasionally up to twenty-eight, internal cross-walls (septa). Asexual reproduction occurs in conspicuous black pycnidia that produce smooth, colourless, ellipsoidal conidia. Chemically, the genus is known to contain rhizocarpic acid, epanorin and various unidentified pigments, alongside secondary metabolites derived from its host lichens. [5]
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