Pannaria Isabellina

''Phormopsora'' is a fungal genus in the family Pannariaceae. It comprises a single species, ''Phormopsora isabellina''. The genus was proposed in 2020 based on molecular and morphological studies of a lichen previously classified in the genera '' Psoroma'' and '' Pannaria''. ''Phormopsora'' is characterised by its large, scale-like structures called that form pale grey rosettes, and by the presence of unique lichen substances not found in other members of its family. The species is primarily found in southern South America, particularly in Chile, where it grows on the trunks of evergreen '' Nothofagus'' trees in humid, temperate rainforests. Its distinctive features include well-developed structures containing nitrogen-fixing cyanobacteria, and with a distinctive outer wall that has irregular swellings and thread-like extensions at the tips.

Taxonomy

Both the genus ''Phormopsora'' and its species were described as new to science in 2020 by the lichenologists Arve Elvebakk, Soon Gyu Hong, and Chae Haeng Park. The genus name comes from the Greek words meaning and meaning , referring to its thallus of large, often intertwining .

''Phormopsora isabellina'' was originally described as ''Psoroma isabellinum'' by Edvard August Vainio in 1899, based on a specimen collected in Chile. The holotype specimen was collected by Franz Wilhelm Neger in 1897 at an elevation of in the Andean forest regions of Chile. It is housed in the herbarium of the University of Turku (TUR-V), with an isotype in the Botanische Staatssammlung München (M).

The taxon was later transferred to the genus '' Pannaria'' as ''Pannaria isabellina'' by Elvebakk and Bjerke in 2005. Molecular phylogenetics analysis in 2020, based on internal transcribed spacer, nuclear large subunit rRNA, mitochondrial small subunit rRNA, and MCM7 genes, showed it formed a distinct lineage separate from ''Pannaria'', leading to its placement in the new genus ''Phormopsora''.

The species epithet ''isabellina'' refers to the isabelline (pale grayish-yellow) colour of the lichen thallus.

''Phormopsora'' is distinguished from related genera in the Pannariaceae by its content of norstictic and connorstictic acids (unique in the family), large branched chlorobiont squamules with large foliose cephalodia, and perispores with long extensions.

Phylogenetically, ''Phormopsora'' forms a sister group to the genus ''Pannaria''. In multi-locus analyses, it clusters with the genus '' Hispidopannaria'', and together they form a sister group to ''Pannaria''. However, this relationship is not consistently maintained across all single-gene phylogenies, indicating a complex evolutionary history.

Description

''Phormopsora'' is characterised by a thallus that is large-, meaning it is composed of small, scale-like structures called . These squamules are typically in diameter, irregularly branched, and form pale grey rosettes. The thallus is often surrounded by a distinct prothallus, which is a thin layer of fungal hyphae extending beyond the main body of the lichen. The upper , or outer layer, of the squamules is , consisting of fungal cells with thick walls arranged in a tissue-like manner.

A unique feature of ''Phormopsora'' is the presence of large, to cephalodia. Cephalodia are specialised structures containing cyanobacteria, which are capable of fixing nitrogen. In ''Phormopspora'', these structures are particularly well-developed and can be easily seen on the lichen surface.

Apothecia (fruiting bodies) are common in ''Phormopsora''. They have rufous brown (the spore-producing surface) with - margins, meaning the edges are finely notched and grooved. The hymenium, the fertile layer of the apothecium, turns blue when treated with iodine (IKI+ blue).

The asci, structures that produce and contain spores, do not have internal amyloid structures (structures that turn blue-black when treated with iodine). The spores themselves are ellipsoid and surrounded by a distinctive (outer spore wall). This perispore is described as , meaning it has irregular swellings or protuberances, and features long, (thread-like) extensions at the tips.

''Phormopsora'' is notable for its unique chemistry among the family Pannariaceae. It contains norstictic and connorstictic acids, which can be detected through thin-layer chromatography. These lichen substances are not found in any other genus within the family, making them a key diagnostic feature for ''Phormopsora''.

Habitat and distribution

''Phormopsora isabellina'' is primarily found in southern South America, with its main distribution in Chile and a single reported occurrence in Argentina. The species is most common in the Los Lagos (X) and Aisén (XI) regions of Chile, becoming rarer in the Magallanes (XII) region further south. Its northern limit is in the Nahuelbuta National Park in the Araucanía (IX) region. ''P. isabellina'' is closely associated with evergreen forests, particularly those dominated by '' Nothofagus betuloides'' and '' N. dombeyi''. It is almost exclusively found growing on the trunks of these evergreen ''Nothofagus'' species, demonstrating a strong preference for this specific habitat. The lichen grows in the humid, temperate rainforest environments characteristic of these regions, typically at moderate elevations.

References

{{Taxonbar , from=Q128062068 , from2=

Pannariaceae
Peltigerales genera
Lichen genera
Taxa described in 2020
Taxa named by Arve Elvebakk