Verrucoccum V. Atienza, D. Hawksw. & Pérez-Ort., Mycologia 113(6): 1236 (2021)
Index Fungorum number: IF 841075, MycoBank number: MB 841075, Facesoffungi number: FoF 15896
Type – Verrucoccum coppinsii V. Atienza, D. Hawksw. & Pérez-Ort.
Etymology – From Verruca (Latin, wart) and -coccus (Latin, spherical). Named after the characteristic warty appearance of the outer wall ornamentation of ascomata and conidiomata.
Diagnosis – The only genus of lichenicolous fungi so far known in Dictyosporiaceae. It is distinguished microscopically from the morphologically superficially similar, but phylogenetically distant, genera Didymocyrtis, Endococcus, and Polycoccum, which also have 1-septate, brown ascospores in that the exposed outer walls of cells of the ascomata and conidiomata are unevenly thickened, giving it an ornamented warty appearance.
Description – Mycelium immersed in the thallus of the host, subhyaline. Sexual morph: Ascomata perithecioid, brown-black, subglobose with a rough surface, ostiolate; ascomatal wall thick, of polygonal pseudoparenchymatal cells forming a textura angularis in surface view, in section composed of an outer layer of dark brown cells with unevenly thickened walls, giving it a warted appearance, and an inner layer continuous below the centrum and composed of thin-walled, hyaline cells with evenly thickened walls. Interascal filaments cellular pseudoparaphyses, branched and anastomosed, persistent, short-celled, not swollen at the ends, septate, interascal gel I−, K/I−. Asci elongate-clavate to subcylindrical with a short ocular chamber, short-stalked, bitunicate in structure, discharge fissitunicate, contents I−, K/I−, or reddish, (4–)6–8-spored. Ascospores uni to biseriate, soleiform, rounded at the apices, 1-septate, golden brown to reddish brown, thick- and smooth-walled. Asexual morph: Conidiomata pycnidial immersed to sessile, arising in contiguous groups associated with ascomata, ostiolate, at first hyaline to pale brown, later becoming dark brown to black, globose; in vertical section multi-layered wall, cells pseudoparenchymatous, forming a textura angularis. Conidiophores absent. Conidiogenouscell lining the inner wall of the pycnidial cavity, elliptic to ampulliform, hyaline, smooth, not proliferating, holoblastic. Conidia acrogenous, produced singly, ellipsoid, narrowed to a truncated base, simple, smooth, pale brown to dark brown.
Distribution and ecology – Verrucoccum is recognized here for three species of lichenicolous fungi found on the apothecia or thalli of Lobaria s. lat. (Lobaria s. str. and Yoshimuriella) species. It is currently known from Canada, Central America (most likely Panama), Russia, the United Kingdom, and the United States (Coppins 2015; Spribille et al. 2020).
Notes – Verrucoccum is very similar to Polycoccum and Didymocyrtis (Ertz et al. 2015) in having perithecioid ascomata, bitunicate asci, 1-septate, brown ascospores, and a lichenicolous lifestyle but differs from those genera in that the cells of the ascomata wall, which are polygonal and dark brown, have unevenly thickened walls, giving a warted appearance, and are not radially compressed in vertical sections with evenly thickened cell walls. Didymocyrtis also differs in having a phoma-like conidial morph, evenly thick-walled cells, enteroblastic conidiogenous cells, and hyaline conidia. Two genera of fungicolous fungi, Immotthia and the recently introduced Sajamaea, have been shown to belong to Dictyosporiaceae and share some morphological similarities with Verrucoccum (Piątek et al. 2020; Jiang et al. 2021) while differing in others. The sexual morphs of Immotthia are characterized by gregarious ascomata, with an inconspicuous pore-like ostiole, a multilayered ascomatal wall, composed of evenly thickened pseudoparenchymatous cells, and arising from a carbonaceous hypostroma. Immotthia species mostly occur on Annulohypoxylon, Hypoxylon, and Pestalopezia species, hosts that are associated with diverse plant hosts or saprobes on decaying wood. Verrucoccum, in contrast, has perithecioid ascomata with a conspicuous ostiole, arising singly or in groups on lichen thalli, and an ascomatal outer wall of dark brown cells with unevenly thickened walls. Sajamaea is only known as an asexual morph, and the asexual morph of Verrucoccum differs from Sajamaea and also Immotthia asexual morphs in having uniloculate conidiomata with holoblastic conidiogenous cells, rather than uniloculate to multiloculate conidiomata with enteroblastic (phialidic) conidiogenous cells. No asexual morph is known in most Immotthia species, but the putative asexual coniothyrium-like morph of I. atrograna, the only species of the genus with a known asexual morph, differs from Verrucoccum in having pycnidial conidiomata arising in groups or developing in multiloculate stromata as well as enteroblastic (phialidic) conidiogenous cells with evident collarettes (Hyde et al. 2017).
The asexual morph of Verrucoccum is somewhat similar to that of Pseudocyclothyriella (Jiang et al. 2021). Both genera have uniloculate pycnidial conidiomata, but Pseudocyclothyriella differs in that the conidiomata wall is multilayered and composed of scleroplectenchymatous cells, the outer layer not with unevenly thickened walls, and a minutely papillate ostiole filled with hyaline periphyses.
Species