Arthopyrenia is a genus of fungi in the family Trypetheliaceae. It was formerly classified in the eponymic family Arthopyreniaceae, but molecular phylogenetics studies showed that the type species, Arthopyrenia cerasi, was a member of the Trypetheliaceae. Arthopyrenia fungi typically form inconspicuous films embedded within tree bark and produce tiny, flask-shaped fruiting bodies covered by dark, shield-like caps. The genus includes both lichen-forming species (those that partner with algae) and non-lichenized species, with about 100 currently recognized species found primarily on bark and wood substrates.
Arthopyrenia forms an immersed thallus, essentially a film sunk into the outer bark, which is usually inconspicuous or only slightly paler than the surrounding tissue and spreads in a diffuse patch. It is not lichenised (i.e. it lacks a visible partnership with algae). The sexual fruit bodies are perithecia (flask-shaped structures with a minute pore), circular to elliptical in surface view. They are covered by a dark, often laterally spreading, clypeate âÂÂa shield-like cap made of compacted fungal hyphae intermingled with bark cellsâÂÂand surrounded internally by a thin, usually colourless (the fruit-body wall). The hyphae are dark brown and react K+ (greenish) in potassium hydroxide. The tissue between and above the asci (the ) consists of robust, thick-walled âÂÂsterile threads that are sparsely branched, occasionally connected to one another (anastomosing), and only distantly partitioned by cross-walls; the gelatinous matrix of the hymenium is iodine-negative (IâÂÂ).
The asci are , meaning they have two functional wall layers that separate during spore release; they are roughly cylindrical, with an apical (a small, frequently conical cap-like apparatus), and do not stain in iodine (IâÂÂ). Each ascus bears eight spores. The ascospores are clavate to cylindric-clavate (club-shaped to narrowly club-shaped), with one or three cross-walls (septae) and a strong narrowing at each septum; they are colourless and smooth when young, sometimes becoming faintly brown and minutely warted in old age. A broad, persistent gelatinous sheath surrounds each spore, a feature that can aid recognition in section.
Asexual reproduction occurs in pycnidiaâÂÂminute, blackish, flask-like structures whose walls contain the same dark pigment as the perithecial involucrellum. The conidiogenous cells (which produce the asexual spores) are variably shapedâÂÂcylindrical, flask-shaped (), or nearly sphericalâÂÂand often proliferate percurrently, extending through the old opening to make a new one like the telescoping of a pen. The resulting conidia are colourless, cylindrical to bacilliform (rod-like), and either lack septae or have three; some species produce two distinct asexual spore types (two anamorphs). No secondary metabolites are detected by thin-layer chromatography.
Arthopyrenia includes both lichenised and saprobic species. Where lichenised, the photobiont is a trentepohlioid alga; in other species no is present. The thallus is usually crustose and largely immersed in the bark or wood, but in some taxa it is reduced to a thin, (cottony) cover formed by a black (a superficial mat of hyphae), and it can also be absent.
The sexual structures are perithecial ascomata that appear circular to ellipsoid in surface view. A dark-brown, (shield-like) overlies the fruiting body and is composed of compressed fungal hyphae mixed with host bark cells. The true ascomatal wall is black and becomes discontinuous beneath the . A thin, usually colourless surrounds the central cavity. The hamathecium comprises branched, anastomosing, sometimes bead-like that are typically non-amyloid; in some species these elements partly dissolve, and the remaining material may stain amyloid. are also present around the ostiole.
The asci are (double-walled), to , with an apical ; they are non-amyloid and contain eight ascospores. The ascospores are usually hyaline (becoming brownish with age in some species), pyriform to clavate, and 1âÂÂ3-septate with true septa (eusepta); walls may bear minute wart-like ornamentation. Reported spore dimensions are about 4âÂÂ16 à12âÂÂ50 üm. Asexual reproduction occurs in blackish pycnidia producing conidia that are simple or 1âÂÂ3-septate, variously oblong, ovoid, , or thread-like. No lichen secondary metabolites are known from the genus.
, Species Fungorum (in the Catalogue of Life) accepts 99 species of Arthopyrenia: