Acrocalymma estuarinum M.S. Calabon, E.B.G. Jones & K.D. Hyde, sp. nov.

Index Fungorum Number: IF 902387; Mycobank number: MB 902387; Facesoffungi number: FoF 15062; Fig. 1

Etymology – In reference to the estuarine habitat where the fungus was found.

Holotype – MFLU 24-FT1207 24-0263

Saprobic on submerged decaying wood. Sexual morph: Not observed. Asexual morph: Ceolomycetous. Conidiomata 120–185 × 50–75 μm, white, solitary to gregarious, immersed, pycnidial, globose to subglobose, unilocular, glabrous and ostiolate. Ostiole 30–45 μm diam., centrally located. Peridium 8.5–17 μm thick, composed of thick-walled, dark brown cells of textura globulosa in the outer layer, become hyaline cells of textura angularis to globosa in the inner layer. Conidiophores reduced to conidiogenous cells or a supporting cell. Conidiogenous cells 12–15×2–3 µm, hyaline, enteroblastic, ampulliform to doliiform, smooth-walled. Conidia 17–22 × 2.5–3.5 (x̅=19.2×3.1 μm, n=20), hyaline, cylindrical with subobtuse apex and base, straight, aseptate, smooth-walled, guttulate, with flaring mucoid apical appendage (2–4 μm diam.), visible in water mounts.

Culture characteristics – colonies on MEA reaching 30–35 mm diam. at 25 °C after 1 month, flat, dry, rough, margin entity to undulate and irregular; from above, light yellow at the margin, light brown in the middle; from below, light yellow at the margin, brown in the middle; not producing pigmentation in the culture.

Material examined – Thailand, Samut Songkhram, Mueng Samut Songkhram, on submerged decaying wood, 8 September 2020, M.S. Calabon, SS109 (MFLU 24-0263, holotype); ex-type MFLUCC 24-0276.

GenBank accession numbers – ITS: PP886241; LSU: PP886242; tef1-α: PP908504

Notes – The combined SSU, LSU, ITS, and tef1-α phylogenetic tree shows that Acrocalymma estuarinum clustered within Acrocalymma and a sister taxon to A. ampeli (MFLUCC 20-0159; MFLUCC 19-0288). However, Acrocalymma estuarium differs from the latter in having a longer conidiomata (120–185×50–75 μm vs. 80–120 × 150–180 µm) and narrower conidia (17–22×2.5–3.5 vs. 17–19×5.5–6.5 μm) with sub-obtuse apex and base. Acrocalymma estuarinum is the first species of Acrocalymma associated with estuarine environment and the fifth species to be reported in aquatic habitats (Zhang et al. 2012; Dong et al. 2020; Boonmee et al. 2021; Calabon et al. 2022, 2023a, b).

Figure 1 – Acrocalymma estuarinum (MFLU 24-0263, holotype). a Appearance of immersed conidiomata on wood surface. b, c Vertical section of conidioma. (c) Section through the peridium. (d)–(g) Conidiogenous cells. (h)–(l) Conidia with appendages. (m) Germinated conidium. Colony on MEA: (n) obverse. Scale bars: (a)=200 μm, (b)=50 μm, (c)–(g)=10 μm, (h)=20 μm, (i)–(l)=5 μm. Scale bars: d, e, g=50 μm, f=20 μm, h–j=30 μm, k–n=5 μm, o=10 μm