Petractis
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| Petractis | |
|---|---|
 | |
| Fruiting bodies of Petractis clausa | |
Scientific classification  | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Lecanoromycetes |
| Order: | incertae sedis |
| Family: | incertae sedis |
| Genus: | Petractis Fr. (1845) |
| Type species | |
| Petractis exanthematica | |
| Species | |
Petractis is a small genus of lichen-forming fungi of uncertain familial and ordinal placement in the Lecanoromycetes.[1] These inconspicuous lichens grow as thin crusts embedded within rock surfaces, partnering with cyanobacteria to form barely visible films that are primarily detected by their small, star-shaped fruiting bodies. The genus contains two species that typically inhabit calcareous rocks, where their fruiting structures create distinctive pits in the stone surface after they decay.
The genus was circumscribed by the mycologist Elias Magnus Fries in 1845. In his brief original description, Fries characterised Petractis as having a stellate (star-shaped) exciple with a fissured margin. He distinguished two forms within his concept of the genus: P. exanthematica (the type species), described as the calcareous form, and P. clausa, noted for its somewhat colourless thallus. Fries classified the genus within his group "Excipula thallinodes" and noted its saxicolous (rock-dwelling) habitat.[2]
In 2021, Damien Ertz and colleagues used multilocus DNA data to reassess relationships within the family Gyalectaceae. They found that Petractis luetkemuelleri and P. nodispora form a lineage remote from the type species P. clausa and instead cluster next to the genus Ramonia. Both of these limestone‑dwelling species partner with a trentepohlioid (green‑algal) photobiont, whereas P. clausa houses cyanobacteria. Because of this clear genetic and ecological divergence, the authors created the new genus Neopetractis for the two displaced species, designating N. luetkemuelleri as the type and making the necessary new combinations. Their study also transferred P. crozalsii to Gyalecta.[3]