Arthopyrenia


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 and non-lichenized species, with about 100 currently recognized species found primarily on bark and wood substrates.

Description

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. The sexual fruit bodies are perithecia, circular to elliptical in surface view. They are covered by a dark, often laterally spreading, clypeate —a shield-like cap made of compacted fungal hyphae intermingled with bark cells—and surrounded internally by a thin, usually colourless . The hyphae are dark brown and react K+ in potassium hydroxide. The tissue between and above the asci consists of robust, thick-walled —sterile threads that are sparsely branched, occasionally connected to one another, and only distantly partitioned by cross-walls; the gelatinous matrix of the hymenium is iodine-negative.
The asci are, meaning they have two functional wall layers that separate during spore release; they are roughly cylindrical, with an apical , and do not stain in iodine. Each ascus bears eight spores. The ascospores are clavate to cylindric-clavate, with one or three cross-walls 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 pycnidia—minute, blackish, flask-like structures whose walls contain the same dark pigment as the perithecial involucrellum. The conidiogenous cells are variably shaped—cylindrical, flask-shaped, or nearly spherical—and 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, and either lack septae or have three; some species produce two distinct asexual spore types. No secondary metabolites are detected by thin-layer chromatography.

Description

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, cover formed by a black , and it can also be absent.
The sexual structures are perithecial ascomata that appear circular to ellipsoid in surface view. A dark-brown, 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 , to, with an apical ; they are non-amyloid and contain eight ascospores. The ascospores are usually hyaline, pyriform to clavate, and 1–3-septate with true septa ; walls may bear minute wart-like ornamentation. Reported spore dimensions are about 4–16 × 12–50 μm. Asexual reproduction occurs in blackish pycnidia producing conidia that are simple or 1–3-septate, variously oblong, ovoid,, or thread-like. No lichen secondary metabolites are known from the genus.

Species

, Species Fungorum accepts 99 species of Arthopyrenia: