Helicoarctatus aquaticus Y.Z. Lu, J.C. Kang & K.D. Hyde
Index Fungorum number: IF 554831; Facesoffungi number: FoF 04708
Etymology: “aquaticus” referring to aquatic habitat of this fungus.
Holotype: MFLU 17–1136
Saprobic on decaying wood in a freshwater stream. Sexual morph: Undetermined. Asexual morph: Hyphomycetous, helicosporous. Colonies on the substratum superficial, effuse, gregarious, white. Mycelium composed of partly immersed, partly superficial, brown to dark brown, septate, branched hyphae, with masses of crowded, glistening conidia. Conidiophores macronematous, mononematous, setiform, cylindrical, unbranched, septate, 195–405 μm long, 5–11 μm wide at bottom, tapering to 2–3 μm wide at apex, brown to dark brown, smooth-walled. Conidiogenous cells holoblastic, mono- to polyblastic, determinate, discrete, denticulate, arising laterally from lower portion of the conidiophores as tiny tooth-like protrusions (3–7.5 μm long, 1.5–3.5 μm wide), with each bearing 1–2 tiny sporogenous conidiogenous loci, hyaline, smooth-walled. Conidia solitary, pleurogenous, helicoid, rounded at tip, 27–38 μm diam. and conidial filament 4–5 μm wide (x¯ = 33 × 4.5 μm, n = 20), 185–255 μm long, 16–20-septate, tightly coiled 3–4 times, will not becoming loosely in water, guttulate, hyaline, smooth-walled. (Lu et al. 2018)
Culture characteristics: Conidia germinating on water agar and germ tubes produced from conidia within 12 h. Colonies growing on PDA, circular, with a center slight umbonate surface, edge entire, reaching 26 mm in 3 weeks at 28 °C, pale brown to brown. Mycelium superficial and partially immersed, branched, septate, hyaline to pale brown, smooth.
Material examined: THAILAND, Trat, Amphoe Ko Chang, Yuttha Navi Ko Chang Memorial, on submerged decaying wood in a freshwater stream, 27 April 2017, Yong-Zhong Lu, TW06–1 (MFLU 17–1136, holotype; HKAS 100807, isotype), ex-type living cultures, MFLUCC 17–1996, TBRC.
Notes: Helicoarctatus aquaticus forms a helicosporous asexual morph on the natural decaying woody substrate and is morphologically similar to Helicosporium species as conidiophores are setiform, conidiogenous cells are discrete, arising laterally from lower portion of the conidiophores as tiny tooth-like protrusions, with each bearing 1–2 tiny sporogenous conidiogenous loci. However, H. aquaticus differs from Helicosporium species by its larger conidia. Phylogenetically, H. aquaticus shares a close relationship to Neohelicoma fagacearum (Lu et al. 2018). (Notes from Lu et al. 2018)