Xenosphaeropsis F. Liu, Crous & L. Cai, gen. nov.

MycoBank number: MB 840272; Index Fungorum number: IF 840272; Facesoffungi number: FoF12731;

Etymology: Xeno = ξένος in Greek, alien, distinct; sphaeropsis = sphaeropsis-like conidia.

Conidiomata pycnidial on agar surface or immersed, subglobose or more or less flattened at the apex, solitary or aggregate in small numbers, thick-walled. Ostioles poroid, inconspicuous. Conidiogenous cells subglobose, lining wall of pycnidium, possibly proliferating percurrently. Conidia brown, smooth-walled, aseptate, variable in shape, clavate to subglobose or irregular, flattened at bottom.

Type species: Xenosphaeropsis pyriputrescens (C.L. Xiao & J.D. Rogers)F. Liu, Crous & L. Cai

Notes: Zhao et al. (2022) introduced Xenosphaeropsis as a monotypic genus within Phacidiaceae, Phacidiales in Leotiomycetes, with Xenosphaeropsis pyriputrescens as the type species based on LSU, ITS and rpb2 multi-gene phylogeny. Xenosphaeropsis pyriputrescens was initially described as Sphaeropsis pyriputrescens (Botryosphaeriaceae, Botryosphaeriales) in Dothideomycetes from a fruit rot on pears in the USA based only on morphology (Xiao and Rogers 2004). However, the initial study did not provide any data on the cultures of either the designated holotype or the isotype (Xiao and Rogers 2004). As the holotype and isotype of Sphaeropsis pyriputrescens could not be traced, Zhao et al. (2022) studied the ex-paratype (ATCC MYA-2947) of S. pyriputrescens in Xiao and Rogers (2004) and provided sequence data. Xenosphaeropsis is morphologically similar to Sphaeropsis in having subglobose pycnidia, subglobose to globose conidiogenous cells and hyaline to brown conidia (Xiao and Rogers 2004, Zhao et al. 2022). This ex-paratype of S. pyriputrescens clustered with three other reference isolates in a separate clade within Phacidiaceae, Phacidiales in the multi-gene phylogeny (LSU, ITS and rpb2) and a novel genus, Xenosphaeropsis was introduced to accommodate these four isolates (Zhao et al. 2022). Xenosphaeropsis showed phylogenetic distance and several morphological differences from other genera in Phacidiaceae and also showed a few morphological similarities to the taxa in Phacidiaceae in having subglobose, separate to aggregate conidiomata, hyaline conidiophores reduced to conidiogenous cells and smooth-walled, hyaline to brown conidia (Crous et al. 2014). Since Xenosphaeropsis is a monotypic genus, the paratype isolate of its only member, Xenosphaeropsis pyriputrescens, clustered with three other isolates from pears and apple in the multi-gene (LSU, ITS and rpb2) phylogenetic tree (Zhao et al. 2022). Xenosphaeropsis pyriputrescens has been reported as a pathogen causing fruit rot and postharvest diseases on pears (Pyrus communis) in British Columbia and Washington (Xiao & Rogers 2004, Sholberg et al. 2009). It is also reported as a pathogen on apple (Malus spp.) and crabapple (Malus sylvestris) trees causing fruit rot, canker, twig dieback and postharvest diseases in Washington and New York (Xiao & Rogers 2004, Xiao & Boal 2005, Kim & Xiao 2008, Kim et al. 2013, 2014, Xiao et al. 2014).

Species