Collemopsis is a fungal genus in the family Lichinaceae. It comprises the single species Collemopsis schaereri, a cyanolichen. Originally described in 1852 and later placed in Psorotichia, the species was shown through molecular studies to represent a distinct lineage, prompting the reinstatement of Collemopsis as a separate genus in 2024. The lichen forms dark, crustose growths on calcareous and other mineral-rich rocks that turn gelatinous when wet, with small fruiting bodies ranging from partly immersed to surface-sitting. Widespread across the Northern Hemisphere from boreal to subtropical zones, it typically inhabits well-lit rock faces that are periodically moistened and can also grow on mortar and brick.
Subsequent molecular work showed that Psorotichia as then understood is divided into five distantly related clades. Material identified as C.schaereri forms a clade together with species of Pycnolemma and Peltolemma, which share the presence of both apothecia and pycnoascocarps . Although Ellis had earlier illustrated the ascomata of C.schaereri as typical apothecia, pycnoascocarps were repeatedly observed in the material revised for the molecular study, though not in the lectotype; because of this inconsistency, this character was not used in ancestral state reconstructions. The new phylogenetic results showed that the species long treated as Psorotichia schaereri is not closely related to P.murorum, the type species of Psorotichia. On this basis, Collemopsis has been reinstated as a separate genus, resurrected from synonymy with Psorotichia to accommodate the single, variable and widely distributed species Collemopsis schaereri.[8]
Description
Collemopsis schaereri forms a dark, usually blackish to deep brown thallus that adheres closely to the rock surface. The thallus is crustose, forming a thin crust, and in some specimens it develops thicker blocks that can become somewhat scale-like (subsquamulose). Parts of the surface may turn grey and finely powdery ( pruinose ), especially in older areas. When wet, the thallus becomes distinctly gelatinous. It is fastened to the substrate by fine fungal strands ( rhizohyphae ). Internally, the thallus lacks a differentiated outer cortex (it is ecorticate ) and consists of tightly packed, small-celled fungal tissue ( paraplectenchyma ) forming a dense network. The photosynthetic partner is a single-celled cyanobacterium whose cells are surrounded by thin, yellowish-brown gelatinous sheaths.[8]
Collemopsis schaereri usually grows on calcareous or otherwise mineral-rich rock, only rarely on acidic substrates, and can also occur on artificial materials such as mortar and brick. It favours inclined, well-lit rock faces that are temporarily or occasionally moistened by seeping water. The species is widespread in the Northern Hemisphere, from boreal to subtropical regions, while older records from the Southern Hemisphere still require confirmation.[8]
↑ Nylander, W. (1869). Synopsis Methodica Lichenum Omnium hucusque Cognitorum, Praemissa Introductione Lingua Gallica[A Methodical Synopsis of All Lichens Known to Date, Preceded by an Introduction in French] (in Latin). Vol.2. pp.1–64 [38].
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