Arnaudiella Petr., Annls mycol. 25(3/4): 339 (1927).
Index Fungorum number: IF 311; Facesoffungi number: FoF 06749, 10 morphological species (Species Fungorum 2022), no molecular data available.
Saprobic on stems forming small dark spots, superficial mycelium absent. Sexual morph: Thyriothecia subglobose to circular, solitary, scattered, or in small groups of two, superficial, membranaceous, or slightly carbonaceous, black to black brown, lower peridium poorly developed, with a central, slightly raised, prominent, darkened, papilla up to 19 μm high, easily separated from host surface; in section subconical. Upper wall comprising rows of cuboid radiating cells which form parallel lines from the central ostiole to the outer rim. Peridium comprising a single substratum of 3–4 layers of compressed brown-walled ellipsoidal cells of textura angularis. Hamathecium of parallel arranged asci inclined from the base and rim towards the central ostiole and sparse pseudoparaphyses. Asci 8-spored, bitunicate, fissitunicate, obclavate, short pedicellate, ocular chamber not obvious, not bluing in IKI. Ascospores overlapping uniseriate or biseriate, oval to broad ellipsoidal with rounded ends, brown, two-celled, smooth-walled. Asexual morph: Xenogliocladiopsis (Adapted from Crous and Kendrick 1994; Wu et al. 2011).
Type species: Arnaudiella caronae (Pass.) Petr.
Notes: Arnaudiella is characterised by subglobose to circular, solitary thyriothecia, obclavate, short pedicellate asci, and overlapping uniseriate or biseriate, oval to broad ellipsoidal two-celled, smooth-walled ascospores. Arnaudiella was referred to Microthyriaceae based on the effortlessly separating thyriothecia with a central ostiole, bitunicate obclavate asci and two-celled brown ascospores (Petrak 1927). Wu et al. (2011) could not find the holotype material of A. caronae and examined a specimen of H. rechinger from PDD and accepted Arnaudiella in Microthyriaceae. Müller and Arx (1962) provided illustration of three species of Arnaudiella but did not illustrate the type species. Swart (1986) provided illustration of several Microthyrium-like taxa and redescribed Arnaudiella bancroftii. Crous and Kendrick (1994) added the new species A. eucalyptorum from Eucalyptus leaves in South Africa, having a Xenogliocladiopsis eucalyptorum hyphomycetous asexual morph. Arnaudiella resembles Seynesiella in having similar ascospores and thyriothecial characters (Swart 1986). Arnaudiella also resembles Tothia in having similar thyriothecia but differs in the arrangement of thyriothecial cells, asci and ascospores. In the phylogenetic analysis of Wu et al. (2011) based on SSU and LSU sequence data, Tothia clustered outside Microthyriaceae hence, the authors suggested that the placement of Arnaudiella also needs to be confirmed based on molecular data. Currently, Arnaudiella is a distinct genus in Microthyriaceae but molecular data is needed to confirm the taxonomic placement of the genus. Arnaudiella also needs epitypification.
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