Porina mayottensis Debaene & Ertz 2026, sp. nov.

Porina mayottensis Debaene & Ertz sp. nov. Fig. 11 Type. MAYOTTE • South of Tsararano, Summit of Mount Bépilipili, 12°52'52.2"S, 45°10'09.2"E, alt. 659 m, humid mountainous forest, 03 Oct. 2017; Ertz 22081 A (holotype: MAO; isotype: BR 5030171995824). Etymology. The epithet refers to the apparent restriction of this species to Mayotte. Diagnosis. This species differs from Porina mazosioides Lücking & Vězda in having less protruding perithecia (lens-shaped to hemispherical in P. mayottensis vs. hemispherical to wart-shaped in P. mazosioides); the absence of distinct verrucae on the thallus; slightly broader ascospores (5–8 µm in P. mayottensis vs. 5–6 µm in P. mazosioides); and the presence of both angular-rounded and rectangular photobiont cells, often occurring on the same thallus. Description. Thallus epiphyllous; small and dispersed or sometimes confluent, ca. 0.5–10 mm wide, and ca. 20 µm thick; sometimes with a whitish translucent prothallus (ca. 0.05 mm wide); finely rugose, encrusted with calcium oxalate crystals; matt to slightly glossy; greyish green to yellowish green. Photobiont rectangular cells, forming radiate plates and / or angular-rounded cells, irregularly arranged; ca. 10–16 (– 21) × (2 –) 3–4 µm (n = 22) when rectangular and (5 –) 8–15 (– 19) × 3–5 (– 8) µm (n = 66) when angular-rounded. Perithecia superficial, moderately delimited from thallus; immature perithecia lens-shaped and mature perithecia lens-shaped to hemispherical; surface smooth to rough, glabrous; ca. 0.3–0.6 mm diam. (n = 30), and ca. 120–140 µm high; covered by ca. 10–20 µm thick algiferous thallus layer; pale yellow to orange, periostiolar area slightly darker; apex convex to slightly applanate, ostiole inconspicuous. Crystallostratum ca. 10–40 µm thick. Excipulum ca. 10–15 µm thick; hyaline to pale yellow, K + yellow to pale orange. Involucrellum ca. 10–15 µm thick; hyaline to pale yellow, K + pale to bright orange. Hamathecium hyaline; not inspersed; composed of thin, simple paraphyses ca. 1–2 μm diam., and ca. 70–100 µm long. Asci fusiform to obclavate; 95–125 × 19–35 µm (n = 14); 8 - spored; with apical ring structure. Ascospores 7 - septate, oblong to narrowly fusiform (36 –) 42.5–48.5 (– 53) × (5 –) 5.8–7.1 (– 8) µm, ratio L / B (6.4 –) 7.2–8.6 (– 9.8) (n = 143), gelatinous sheath not or poorly visible and thin (ca. 1 µm). Pycnidia not observed. Chemistry not tested for thallus; TLC not performed. Distribution and ecology. The species is known from six different localities in Mayotte. It inhabits the surfaces of leaves in rather dense, humid forests at low to moderate elevations (ca. 370–660 m). Notes. The examined P. mayottensis specimens were recovered in the Porina s. str. clade, showing little intraspecific genetic divergence in both the ITS and mtSSU phylogenies (Figs 2, 3). In the ITS phylogeny, they form a subclade with P. mazosioides and P. aff. mazosioides. Porina mazosioides was the most similar species because it shows both morphological similarity and a close phylogenetic relationship as the sister taxon of P. mayottensis. However, the two species differ mainly in their perithecial and thallus morphology, photobiont morphology, and slight differences in ascospore sizes. Both angular-rounded photobiont cells arranged irregularly and rectangular cells arranged in radiate plates were observed on five of the eight sequenced specimens. This resembles P. rudiuscula (Nyl.) Müll. Arg., in which foliicolous specimens described by Lücking and Vězda (1998) also exhibit different photobiont morphotypes on the same thallus. However, it remains unclear whether these contrasting morphotypes represent two or more Trentepohlia species occurring within the same thallus or morphological variation within a single algal species. Although two different rbc L sequences were not recovered from individual specimens, several samples consistently produced two PCR fragments of similar length that could not be separated using standard amplification protocols. This anomaly could potentially indicate the presence of two different Trentepohlia taxa in the thallus piece used for extraction. Overall, the recovered algal haplotypes were distributed among clades 29 (29: 5 and 29: 6; Fig. 11 E) and 36 (Fig. 11 F), the latter containing only sequences from P. mayottensis specimens (Figs 4, 5). The sequence recovered within algal haplotype 29: 5 clusters with a P. parva specimen, which is plausible because the P. mayottensis specimen appeared to harbour only a photobiont with rectangular cells arranged in radiate plates. Most specimens had relatively small thalli, although one specimen had a larger, confluent thallus. The combination of a distinct phylogenetic position, consistent morphology across specimens, and diagnostic differences supports the recognition of P. mayottensis as a distinct species. Additional specimens examined. MAYOTTE – South of Tsararano • ridge between Mount Bénara and Mount Bépilipili, 12°52'49"S, 45°09'59"E, alt. 580 m, humid ridge forest (mountainous) with rocky outcrops, 03 Oct. 2017; Ertz 22069 A (BR). • ibid., summit of Mount Bénara, 12°52'47"S, 45°09'46"E, alt. 660 m, humid ridge forest (mountainous), 01 Oct. 2017; Ertz 21972 B (BR). • ibid., summit of Mount Bépilipili, 12°52'52.2"S, 45°10'09.2"E, alt. 659 m, humid montane forest, 03 Oct. 2017; Ertz 22079 B (BR). – Choungui • Path of Mount Choungui, 12°57'38.7"S, 45°08'08.4"E, alt. 365 m, dense humid forest, 29 Sep. 2017; Ertz 21856 D (BR). – Mamoudzou • forest reserve of Majimbini, near the governor’s house, 12°45'59.8"S, 45°11'23.7"E, alt. 470 m, dense primary forest, 10 Oct. 2017; Ertz 22321 D, 22321 E (BR). – North West of Bandrele • near summit of Mount Bépilipili, 12°52'54.8"S, 45°10'09.7"E, alt. 611 m, humid montane forest, 01 Oct. 2017; Ertz 22085 A (BR).