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 (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 involucrellum —a shield-like cap made of compacted fungal hyphae intermingled with bark cells—and surrounded internally by a thin, usually colourless exciple (the fruit-body wall). The hyphae are dark brown and react K+ (greenish) in potassium hydroxide. The tissue between and above the asci (the hamathecium ) consists of robust, thick-walled pseudoparaphyses —sterile 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 (I–). [4]
The asci are fissitunicate , meaning they have two functional wall layers that separate during spore release; they are roughly cylindrical, with an apical ocular chamber (a small, frequently conical cap-like apparatus), and do not stain in iodine (I–). 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. [4]
Asexual reproduction occurs in pycnidia—minute, 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 shaped—cylindrical, flask-shaped ( lageniform ), 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 (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. [4]
Description
Arthopyrenia includes both lichenised and saprobic species. Where lichenised, the photobiont is a trentepohlioid alga; in other species no photobiont 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, byssoid (cottony) cover formed by a black subiculum (a superficial mat of hyphae), and it can also be absent. [5]
The sexual structures are perithecial ascomata that appear circular to ellipsoid in surface view. A dark-brown, clypeate (shield-like) involucrellum 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 hamathecium . A thin, usually colourless exciple surrounds the central cavity. The hamathecium comprises branched, anastomosing, sometimes bead-like pseudoparaphyses that are typically non-amyloid; in some species these elements partly dissolve, and the remaining material may stain amyloid. Periphysoids are also present around the ostiole. [5]
The asci are bitunicate (double-walled), pyriform to clavate , with an apical tholus ; they are non-amyloid and contain eight ascospores. The ascospores are usually hyaline (becoming brownish with age in some species), pyriform to clavate, and 1–3-septate with true septa (eusepta); 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, bacilliform , or thread-like. No lichen secondary metabolites are known from the genus. [5]
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