Epilichen
Epilichen is a small genus of lichen-forming fungi in the family Rhizocarpaceae. These parasitic lichens live on other lichens, beginning as thin, crust-like patches that may break into small islands or scales, and in some cases produce no visible body at all except for their reproductive structures. They reproduce through black, disc-shaped fruiting bodies that contain distinctive brown spores with a "doughnut ring" appearance, and can eventually take over the space occupied by their host lichen once it dies.
Taxonomy
The genus was proposed by the American ecologist Frederic Clements in 1909, with E. scabrosus assigned as the type species. Clements originally classified the genus in the family Patellariaceae.Description
Epilichen species parasitise other lichens and begin as thin, crust-like patches that may fracture into island-like or develop minute scales. In some cases the lichen produces no visible thallus at all, emerging only as reproductive bodies on its host. A distinct and a protective outer skin are both absent, and the genus lacks the powdery or bud-like outgrowths that many lichens use for asexual spread. The photosynthetic partner is always a green alga with rounded cells.Sexual reproduction occurs in black, disc-shaped apothecia that lack a, so the only border is the, a dark, compact ring of fungal tissue. A thin brown coats the top of the hymenium, while a thick, dark-brown lies beneath. Threads called weave through the hymenium, branching and re-joining to form a loose net but seldom swelling at the tips. The asci are long, club-shaped sacs; when treated with potassium iodide solution they turn blue, a diagnostic amyloid reaction caused by the and the surrounding gelatine. Each ascus releases brown ascospores divided by a single wall; a torus-shaped thickening encircles the septum, giving the spores a distinctive "doughnut ring" appearance. No asexual pycnidia have been observed in the genus. Chemically, the genus contains two pulvinic acid pigments that lend yellow tones, along with several unidentified secondary metabolites. Although Epilichen is obligately lichenicolous, it may form its own independent thallus once the host lichen's fungal partner dies, effectively inheriting the space it first exploited.