| Pseudocarpon | |
|---|---|
Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Lichinomycetes |
| Order: | Lichinales |
| Family: | Porocyphaceae |
| Genus: | Pseudocarpon M.Schultz & M.Prieto (2024) |
| Species: | P. persimile |
| Binomial name | |
| Pseudocarpon persimile M.Schultz & M.Prieto (2024) | |
Pseudocarpon is a fungalgenus in the familyPorocyphaceae.[1] It comprises the single speciesPseudocarpon persimile, acyanolichen. Described fromlimestone outcrops onGotland in Sweden, the species was later shown bymolecular studies to form a distinctevolutionary line nearWatsoniomyces within Porocyphaceae. The lichen forms tiny scattered patches of dark granular material oncalcareous rocks, with numerous small hemisphericalfruiting bodies that resemble 'fish eyes'. It grows in periodically wetted habitats and is currently confirmed from Sweden and Switzerland, though it is easily overlooked and may be confused with the similarPyrenocarpon thelostoma.
The genusPseudocarpon was created to accommodate a small blackcrustose lichen that had been collected fromcalcareous rocks in several European localities but did not fit any existing genus. Thetype and only known species,Pseudocarpon persimile, wasdescribed fromlimestone outcrops inalvar-like habitat on the island ofGotland in Sweden. The generic name alludes to the resemblance between this lichen andPyrenocarpon thelostoma, with which it can easily be confused in the field.[2]
Fresh collections from Gotland with hemispherical fruiting bodies (apothecia) that resemble small "fish eyes" were shown bymolecular analyses to form a distinctlineage withinPorocyphaceae. These samples cluster nearWatsoniomyces and lie apart fromPorocyphus,Paracyphus andPyrenocarpon, despite their outward similarity. An intensive search for an existing species that matched themorphology andDNA sequences of the Gotland material failed, and soPseudocarpon was introduced as a new genus withP. persimile as its type.[2]
InPseudocarpon persimile thethallus forms very small, scattered patches nestled among other lichens on calcareous rock. The thallus is blackish and crustose, breaking into tinygranules or minuteareoles about 0.1–0.2 mm across. These areoles are very thin and are fixed to the rock by fungal filaments (rhizohyphae) that sometimes weave into a slightly gelatinous basal layer. The overall effect is of a dark, finely granular dusting on the stone surface rather than a thick, solid crust.[2]
When viewed in section, the thallus ishomoiomerous andecorticate. This means that, instead of having a distinct outer skin (cortex) and clearly separated layers, the fungal tissue andphotosynthetic partner are intermixed through most of the thickness. The fungalhyphae form a dense, reticulate mesh of short, angular cells that wrap around thecyanobacterial cells. Thephotobiont is a coccoid cyanobacterium with spherical to slightly flattened cells, usually one or two to a sheath. Each cell or pair of cells is enclosed in a thin, yellowish-brown gelatinous envelope, and the cyanobacteria are surrounded by hyphae that form finger-likehaustoria penetrating the sheath. This combination of relatively large, single-celled cyanobacteria and stout, interlocking hyphae setsPseudocarpon apart from some similar genera that have more delicate tissue with smaller cells.[2]
The apothecia are numerous and usually occur one per areole. They begin as small, hemispherical structures and mature into broader,sessile cups about 0.2–0.4 mm in diameter. Each apothecium iszeorine in form: it has a low rim derived both from the thallus (thalline margin) and from a distinct internal ring of fungal tissue (theproper exciple). The outer thalline rim is shallow and rather smooth, while the inner margin is pale and thickened towards the top, becoming reddish brown at the apex. Thedisc itself is narrow, more or less plane rather than distinctly concave, and dark reddish brown. Internally, the hymenium is relatively low for a Porocyphaceae lichen and is underlain by a thin subhymenium. Theparaphyses are straight, robust and distinctlyseptate; they branch and join near their tips and end in slightly widened terminal cells. The asci are narrow, club-shaped to somewhat spindle-shaped, with a slender base, and belong to theLichina type. They are thin-walled but surrounded by a faint bluish gelatinous coat. Each ascus contains eightsimple, colourlessascospores that areellipsoid and small; the spore wall isamyloid, taking on a blue reaction in iodine.[2]
The reproductive development ofPseudocarpon involves pycnoascocarps. Initially, the fungus formspycnidia, which are small flask-shaped cavities that produceasexual spores (conidia). Within these structures, female reproductive hyphae (ascogones) arise beneath the pycnidial cavity. As development proceeds, the pycnidial wall thickens and becomes the proper exciple, theconidiophores disappear, and the entire structure is transformed into a sexual apothecium. The pycnidia observed inP. persimile are broadly pear-shaped and produce simple, terminal conidiophores that give rise to tiny, ellipsoid conidia. Lichen chemistry has not yet been investigated inPseudocarpon usingthin-layer chromatography.[2]
Pseudocarpon persimile was described from limestone outcrops inalvar-like landscapes on the island of Gotland in Sweden, where it forms small patches on exposed rock surfaces. Additional collections from Gotland come from similar open, calcareous habitats, including shooting ranges and alvar areas with thin soil cover over limestone pavement. In these settings the lichen typically grows on exposed limestone that is periodically wetted by surface water.[2]
Matching DNAhaplotypes have been found in material collected on calcareous rock along the banks of theRiver Rhine nearBasel in Switzerland, indicating that the species occurs outside Gotland. Morphologically very similar specimens have also been reported from concrete along theRiver Isar inMunich and from shallowrock pools in north-easternMallorca, although more material is needed to confirm the full extent of the species and its variation. Across this range,Pseudocarpon persimile occupies calcareous substrates near rivers and pools and can tolerate temporary inundation when water levels rise. The species is easily overlooked and can be confused withPyrenocarpon thelostoma,Paracyphus gotlandicus or young thalli ofLemmopsis arnoldiana, and the authors suggest that further examination ofherbarium material assigned to these taxa may reveal additional records ofPseudocarpon.[2]