Helhonia
Helhonia B. Sutton, The Coelomycetes: 600 (1980)
Ascomycota, genera incertae sedis
Saprobic on stems of Sambucus nigra (Adoxaceae). Sexual morph: undetermined. Asexual morph: Conidiomata pale brown, pycnidial, scattered or gregarious, subepidermal to epidermal, immersed to erumpent, subglobose, unilocular, glabrous. Ostiole absent, dehiscence by irregular splits of apical wall. Conidiomatal wall composed of thin-walled, hyaline cells of textura angularis in the basal part, becoming thick-walled, pale brown cells at the upper part. Conidiophores arising from the inner wall layer of conidiomata, hyaline, cylindrical, branched, septate, smooth-walled. Conidiogenous cells hyaline, enteroblastic, phialidic, cylindrical to ampulliform, integrated, less often discrete, determinate, smooth-walled, with minute collarette and channel. Conidia hyaline, cylindrical to fusiform, tapered at one or both ends, 1-septate, smooth-walled, guttulate (adapted from Sutton 1980).
Type species: Helhonia rhamnigena (Fautrey) B. Sutton, The Coelomycetes: 600 (1980)
Notes: Helhonia is monotypic. This genus can easily be confused with Cylindrogloeum, Davisiella, Diplozythiella and Placonemina, because all have septate, fusiform conidia. However, characters of conidiomata, conidiophores and conidiogenous cells and habitat can differentiate these genera. Helhonia has pycnidial conidiomata, while Cylindrogloeum has acervular conidiomata. Davisiella has two types of conidiomatal wall (hyaline, rather thick-walled cells of textura angularis in the outer layers, becoming smaller and compact cells towards inner layers), and 2–3-septate conidia. The conidiomatal wall of Helhonia consists of thin-walled, hyaline cells of textura angularis in the basal part, becoming thick-walled, pale brown cells at the upper part, and the conidia are 1-septate. Davisiella species are fungicolous, while Helhonia rhamnigena is saprobic. In Diplozythiella and Placonemina, the conidiophores are reduced to conidiogenous cells, while in Helhonia, they are hyaline, branched, septate. It is difficult to clarify relationships among these genera due to a lack of molecular data. Fresh collections of Cylindrogloeum, Davisiella, Diplozythiella and Placonemina are needed to place them in a natural classification.
Distribution: France (Sutton 1980).
Helhonia rhamnigena (redrawn from Sutton 1980) a Conidia. b Conidiophores, conidiogenous cells and developing conidia. c Vertical section of conidioma.
References:
Li WJ, McKenZie EHC, Liu JK, Bhat DJ, Dai DQ, Caporesi E, Tian Q, Maharachcikumbura SSN, Luo ZL, Shang QJ, Zhang JF, Tangthirasunun N, Karunarathna SC, Xu JC, Hyde KD (2020) Taxonomy and phylogeny of hyaline-spored coelomycetes. Fungal Diversity 100: pages279–801.
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