Zwackhiomyces Grube & Hafellner, Nova Hedwigia 51(3– 4): 305 (1990).
Index Fungorum number: IF 25388; Facesoffungi number: FoF 07658, 26 morphological species (Species Fungorum 2022), 1 species with molecular data.
Vegetative hyphae not observed. Sexual morph: Ascomata perithecioid, immersed in initial states, semi-immersed at maturity, scattered or in groups of 3–5 pseudothecia, black, subglobose. Ascomatal wall pseudoparenchymatous, dark brown in outer part, brown in middle, and hyaline in inner part; with 5–8 layers of cells; cells rounded in outer parts and ± radially compressed in inner part, granular brown pigments extracellular, turning black or olive-black in K. Hymenial gel I–, K/I–. Paraphysoids abundant, branched and anastomosing. Asci clavate, uniseriate to biseriate, (4–)8-spored, endoascus I–, BCr–. Ascospores ellipsoid, uniseptate, hyaline, verrucose, markedly constricted at septum, slightly heteropolar, upper cell ± rounded, lower cell narrower than upper and slightly attenuated, sometimes upper cells with oil droplets. Ascospore halo indistinct, 0.5 µm thick in water. Asexual morph: Unknown (adapted from Calatayud et al. 2007).
Type species: Zwackhiomyces coepulonus (Norman) Grube & R. Sant.
Notes: Zwackhiomyces is characterised by perithecioid immersed to semi-immersed ascomata, abundant, branched and anastomosing paraphysoids, clavate (4–)8-spored asci and ellipsoid,uniseptate, hyaline, verrucose ascospores. Several authors added new species to Zwackhiomyces (Alstrup 1993; Alstrup and Olech 1993; Harris 1995; Hawksworth and Miadlikowska 1997; Miadlikowska and Alstrup 1995), and five species have been transferred to the genus (Aptroot et al. 1997; Calatayud et al. 2003; Hafellner and John 2006; Hawksworth and Atienza 1994; Hoffmann and Hafellner 2000; Orange 2002). In some species such as Z. arenicola, over mature ascospores are brown and 3-septate (Hoffmann and Hafellner 2000) while in Z. lecanorae the ascospores are simple hence the placement of certain taxa in Zwackhiomyces is doubtful. Zwackhiomyces differs from Arthopyrenia and Didymellopsis in having pigmented excipular cells, formed from granular dark brown pigment deposited between the cells. Pérez-Ortega et al. (2016) provided sequence data for Z. coepulonus. Zwackhiomyces is a distinct genus in Xanthopyreniaceae but more collections with molecular data are need to confirm this placement and its relationship with other genera. Molecular markers available for Zwackhiomyces include LSU and SSU.
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