Megalocystidium Jülich

Xu, Y. L., Cao, Y. F., Liu, S. L., Nakasone, K. K. & He, S. H., 2025, Taxonomy and phylogeny of Stereaceae (Russulales, Basidiomycota): two new genera, nine new species and twenty new combinations, Persoonia 54 (1), pp. 119-145 : 139

Megalocystidium Jülich , Persoonia 10: 139. 1978. emend.

Basidiomes annual, effused to effused-reflexed, adnate, membranaceous, ceraceous to coriaceous. Pilei small, usually curved inwards when dried; abhymenial surface with dense tomentum when juvenile, becoming glabrous with age, greyish brown to dark brown, sulcate and zonate. Hymenophore smooth to tuberculate, greyish orange, light brown, greyish brown, golden brown to brown, not cracked or deeply cracked with age; margin byssoid or thinning out, adnate or slightly elevated, paler than or concolourous with hymenophore. Hyphal system monomitic or dimitic. Generative hyphae simple-septate or nodose-septate, colourless to pale yellow, thin- to thick-walled, smooth. Gloeocystidia present, tubular, vesicular or clavate, colourless to pale yellow, thin to slightly thick-walled, smooth, mostly embedded. Acanthohyphidia present or absent, subclavate to subcylindrical, colourless to pale yellow, thinto thick-walled, with spines at the apical part. Basidia clavate to subcylindrical, colourless, thin-walled, smooth, with four sterigmata. Basidiospores ellipsoid to cylindrical, colourless, thin-walled, smooth or almost so, amyloid, acyanophilous.

Type species: Megalocystidium leucoxanthum (Bres.) Jülich

Notes: The genus was moderately supported in the tree ( Fig. 1 ). Traditionally, Megalocystidium included species with effused basidiomes, nodose-septate generative hyphae, long basidia, large basidiospores and without acanthohyphidia ( Wu 1996). Spirin et al. (2021) transferred Peniophora diffissa to the genus, which has abundant acanthohyphidia. In our phylogenetic analyses, Megalocystidium chinensis , M. wakullum and other two undescribed species with simple-septate generative hyphae and acanthohyphidia formed a sister subclade to M. leucoxanthum subclade. Moreover, Boidin et al. (1979) described Stereum peculiare (syn. M. chinensis , see below) as dimitic, whereas all other species are monomitic. Thus, at present, we prefer to treat the two subclades as a single genus because of the entangled morphological patterns.

Figures

Fig. 1. Phylogenetic tree obtained from maximum parsimony analysis of ITS-LSU sequence data of Stereaceae. Branches are labelled with parsimony bootstrap values (≥ 70 %, first), maximum likelihood bootstrap values (≥ 70 %, middle) and Bayesian posterior probabilities (≥ 0.95, last). Type species of each genus are marked with an asterisk “*”. New taxa are shown in bold with type specimens marked with a number sign “#”.