Chaetosphaeria obovoideaJ.Y. Zhang & Y.Z. Lu, in Zhang, Ma, Xiao, Boonmee, Kang & Lu, Journal of Fungi 8(no. 643): 10 (2022)

Index Fungorum number: IF559696; Facesoffungi number: FoF 11036;

Etymology – Referring to obovoid conidia

Holotype – HKAS xxxx

Saprobic on decaying wood submerged in freshwater habitats. Sexual morph: undetermined. Asexual morph: hyphomycetous. Colonies on natural substrate superficial, effuse, scattered, pale brown, with white and gold masses on the apex of conidiophores. Mycelium is composed of partly immersed, partly superficial, hyaline-to-pale brown, septate, branched hyphae. Conidiophores 93–234(–291) μm long, 3.5–5.3 μm wide at the base, macronematous, mononematous, erect, straight or slightly flexuous, occasionally branched, with intercalary conidiogenous loci, cylindrical, solitary, brown at the base, pale brown or subhyaline towards the apex, septate, smooth-walled, with pale gold or red appendants attached. Conidiogenous cells 13–51 × 3–5.5 μm (x¯ = 33.8 × 4.6 μm, n = 20), mono- to polyphialidic, terminal, integrated, cylindrical, with funnel-shaped collarettes, brown or pale brown to subhyaline or hyaline towards the apex. Conidia 10–14.8 × 5–7.2 μm (x¯ = 12.7 × 6 μm, n = 20), amerospores, aseptate, obovoid, pyriform to broadly clavate, rough-walled, aggregated in large and slimy mass, hyaline, round at the apex, tapering at the base and often with a small prominence.

Culture characteristics – Conidia germinating on PDA within 15 h and hyaline germ tube produced from the base of conidia. Colonies growing on PDA at 25 °C reach 17 mm in three weeks, circular, unbonate, entire, with filamentous, dense, aerial mycelium on the surface, white at the center, pale grey at the edge from above; yellowish to greyish brown to pale brown in reverse from the center to the margin of the colony, and do not produce pigmentation in culture.

Material examined – CHINA, Hainan province, Diaoluo Mountain National Nature Reserve, on decaying wood submerged in a stream, 20 August 2021, W.G. Lin, DL2 (HKAS 123765, holotype; GZAAS 22-0076, isotype), ex-type living cultures, GZCC 22-0085.

GenBank accession numbers – LSU: ON502894, ITS: ON502901.

Notes – In a BLASTn search in GenBank, the closest match to the ITS sequence of our new isolate was Chaetosphaeria sp. (strain JEH-2019) with 97% (MN619651) similarity across 88% of the query sequence. The closest match to the LSU of the new isolate was Chaetosphaeria fusiformis (strain CBS 101429) with 99.21% (AF178554) similarity across 94% of the query sequence. The phylogenetic analysis confirmed that our new isolate of Cobovoidea formed a separate clade within the Chaetosphaeria genus and is a sister clade to Chaetosphaeria sp. (strain JEH-2019) with good support (94% ML/1.00 PP). Thus, we introduced this new isolate as a novel species in the Chaetosphaeria. Additionally, our new species formed a unique asexual morph in the natural substrate and differ from all existing species of Chaetosphaeria in having macronematous conidiophores with pale gold or red appendants attached, hyaline, aseptate and obovoid conidia with prominence at the base. This adds complexity and diversity to the asexual morphs of the Chaetosphaeria genus.

Figure 1. Chaetosphaeria obovoidea (HKAS 123765, holotype). (a,b) Colonies on woody substrate; (c–f) Conidiophores Conidiogenous cells ; (g–j) Conidiogenous cells; (j–l) Conidia; (l) Germinating conidium; (m,n) Culture on PDA from above and below. Scale bars: (c–f) 25 μm; (g–i) 20 μm; (j–l) 10 μm.