Annulatascus thailandensis W. Dong, H. Zhang & K.D. Hyde

Index Fungorum number: IF556954
Etymology – In reference to the host location in Thailand, where the holotype was collected.
Holotype – MFLU 18-1556.
Saprobic on decaying wood submerged in freshwater. Sexual morph: Ascomata 170–200 μm high, 250–300 μm diam, solitary or gregarious, superficial, ellipsoidal or subglobose, black, coriaceous, with a lateral neck, often lying horizontally or obliquely to the substrate surface. Neck long or short, black, curving upwards or lying on the host surface, up to 600 μm long. Ostiole eccentric, lateral, black, periphysate. Peridium 32–37 μm thick at upper part, comprising 5–8 layers of brown to dark brown, thick-walled, compressed cells of textura angularis or round cells; 75–85 μm thick near the base where below the neck, comprising 12–15 layers of pale brown to brown, thin-walled, compressed cells of textura angularis or irregular cells; 3–5 layers of hyaline, compressed cells of textura angularis inwardly. Paraphyses ca 4–5.5 μm diam. near the base, tapering distally, hypha-like, numerous, hyaline, unbranched, septate, constricted at the septa. Asci 275–375 × 13–15 μm (= 310 × 13.7 μm, n = 10), 8-spored, unitunicate, cylindrical, apically rounded, with a long pedicel, up to 130 μm long, with a massive, wedge-shaped, refractive apical ring, 3.5–4 μm high × 5.5–6 μm wide. Ascospores 28–33 × 10.5–11.5 μm (= 30.8 × 11.2 μm, n = 10), uniseriate, hyaline, ellipsoidal to fusiform, straight to curved, 1–2-septate, slightly constricted at the septa, minutely guttulate, thin-walled, with a large, nearly ellipsoidal, mucilaginous sheath, 10–15 μm thick. Asexual morph: Undetermined.

Culture characteristics – On PDA, colony circular with filamentous margin, reaching 30 mm in 35 days at 25°C, brown to white from above, white to pale brown from below, surface rough, dry, raised, with dense mycelia, edge filiform. 

Material examined – THAILAND, Nakhon Si Thammarat Province, on submerged wood in a stream, 10 May 2018, W. Dong hat650 (MFLU 18-1556, holotype), ex-type living culture MFLUCC 18-1248; on submerged wood in a stream, 10 May 2018, W. Dong hat650 (HKAS 105023, isotype), living culture KUMCC 19-0038.

GenBank numbers – ITS: MN733256, LSU: MN733254, SSU: MN733253

Notes – Annulatascus thailandensis fits well within the generic concept of Annulatascus in having a typical massive, apical ring and ellipsoidal to fusiform ascospores (Hyde 1992b, Maharachchikumbura et al. 2016b). In our phylogenetic tree, A. thailandensis clustered with A. hongkongensis with strong bootstrap support. However, A. thailandensis has smaller ascospores (28–33 × 10.5–11.5 μm vs. 35–37.5 × 12.5–15 μm) and longer and thinner asci (275–375 × 13–15 μm vs. 250–275 × 25–30 μm). The ascospores of A. thailandensis are 1–2-septate, whereas those of A. hongkongensis are 3-septate (Ho et al. 1999). Annulatascus thailandensis is also similar to A. saprophyticus in asci and ascospore morphology and they have overlapping ascospore size (Luo et al. 2015). However, they can be separated by characters of ascomata (superficial, with long or short necks, lying horizontally or obliquely to the substrate surface vs. partly immersed, with straight upright necks to the substrate surface), size of asci (275–375 × 13–15 μm vs. 230.5–261 × 13.5–16.5 μm) and septa of ascospores (1–2-septate vs. 0–3-septate) (Luo et al. 2015).