Occultitheca chiangraiensis Louangphan, Phukhams., K. D. Hyde & Bhunjun 2025, sp. nov.

Occultitheca chiangraiensis Louangphan, Phukhams., K. D. Hyde & Bhunjun sp. nov. Fig. 8 Etymology. The name refers to the province where the holotype was collected. Holotype. MFLU 24–0414. Description. Saprobic on early decaying branch. Sexual morph: Ascomata 220–342 × 228–395 μm (x ̄ = 290 × 324 μm, n = 15), immersed, solitary, scattered, globose to subglobose, erumpent through host surface, visible as black dot of ostiole, surrounded by a whitish halo. Clypeus carbonaceous, rudimentary, thick-walled, the ostiolar opening surrounded with black cells. Ostioles centric, ostiolar canal periphysate. Peridium 17–30 μm (x ̄ = 23 μm, n = 20) wide, tightly attached to the host tissue, with two cell layers, outer layer thick-walled, comprising yellowish brown cells of textura angularis, inner layer thin, composed of hyaline cells of textura angularis. Paraphyses 3.7–7.6 μm (x ̄ = 5.4 μm, n = 25) wide, wider at the base, longer than the asci, filamentous, septate, constricted at the septa, embedded in gelatinous matrix. Asci 112–158 × 8.5–13.7 μm (x ̄ = 131 × 11 μm, n = 25), 8 - spored, unitunicate, cylindrical, short pedicellate, apically rounded, with 3.9–5.6 × 2.5–3.7 μm (x ̄ = 5 × 3 μm, n = 18), rectangular to slightly obconic, apical ring, J + in Melzer’s reagent. Ascospores 14.5–17.6 × 6–7.4 μm (x ̄ = 16.3 × 6.7 μm, n = 30), L / W 2.4, oblong to ellipsoidal, uniseriate, brown, inequilaterally unicellular, apical cell 13–15.5 μm (x ̄ = 14.5 μm, n = 30) long, usually with large guttules, brown cell with a mucilaginous sheath covering most of the spore length when mature, with a small, hyaline, rounded, basal cell, 1.3–2.3 μm (x ̄ = 1.8 μm, n = 30), lack of germ slit. Asexual morph: Undetermined. Culture characteristics. Colonies on PDA, reaching 40 mm diam., after 21 days at 25 ° C, circular, entire edge, smooth surface, flat, slightly woolly, smooth margin, above ash white from the centre to white at the edge with concentric rings of woolly; from below: light brown at the centre, white at the margin, with ash white mycelium. Material examined. Thailand, Chiang Rai, Mae Fah Luang District, Mae Salong Nok, on a dead unidentified dicot branch, 16 January 2023, J. Louangphan, CR 1–19 (MFLU 24–0414, holotype); ex-type MFLUCC 25–0158. Host. Unidentified branch (this study). Distribution. Thailand (this study). Notes. Based on multi-gene phylogenetic analyses of ITS, LSU, rpb 2, and tub 2 sequences, Occultitheca chiangraiensis (MFLU 24–0414) clustered with O. rosae (HKAS 102393) and Clypeosphaeria oleae (CPC 36779) with 100 % ML and 1.00 BPP support (Fig. 7). Clypeosphaeria oleae was reported only from the asexual morph (Crous et al. 2019); thus, we could not compare the morphology between the species as we could not obtain the asexual morph of our strain, and therefore the link between them cannot be confirmed. Furthermore, C. oleae lacks rpb 2 and tub 2 data, which is important to confirm its phylogenetic placement. Morphologically, Occultitheca chiangraiensis fits the generic concept of Occultitheca in having immersed ascomata, short pedicellate asci with a J +, apical ring, a long distance between the ascus apex and the uppermost ascospore, and hyaline basal cells attached to brown ascospores (Rogers and Ju 2003; Samarakoon et al. 2022). Our isolate was compared to Occultitheca species as detailed in Table 4. Occultitheca chiangraiensis differs from O. rosae by having smaller ascomata (x ̄ = 290 × 324 μm vs. 370 × 385 μm), a lack of a germ slit, and possesses a thicker mucilaginous sheath compared to O. rosae (Samarakoon et al. 2022). Our strain differs from O. ananasi, which has uniseriate, olive-greenish ascospores becoming 2 - seriate in the middle and thin mucilaginous sheath (Tian et al. 2024). Occultitheca chiangraiensis was also compared to the type species O. costaricensis as it lacks molecular data. Occultitheca chiangraiensis differs by having 1–2 individual ascomata and ascospores with a mucilaginous sheath, while O. costaricensis has 2–12 ascomata in a cluster and ascospores without a sheath (Rogers and Ju 2003). Additionally, some Anthostomella species have similar characteristics in terms of ascoma, asci, and ascospores with draft cells and lack germ slits, such as A. clypeata and A. clypeoides, but differ in a short space of the top ascospore and the ascus apex and shape of the sheath compared to Occultitheca species (Lu and Hyde 2000; Rogers and Ju 2003). Our strain differs by 6 % in the ITS region (30 / 482, 4 gaps), 2 % in LSU (14 / 745, 4 gaps), 15 % in rpb 2 (117 / 798, no gap), 16 % in tub 2 (120 / 754, 22 gap), and 3 % in tef 1 (31 / 915, 1 gap) sequences compared to O. rosae (HKAS 102393). Thus, Occultitheca chiangraiensis is reported as a new species based on morphology and phylogenetic evidence. - Data not available.