Robiniigena hyalinospora Bundhun, Camporesi & K. D. Hyde 2024, sp. nov.

Robiniigena hyalinospora Bundhun, Camporesi & K. D. Hyde sp. nov. Fig. 4 Etymology. The epithet refers to the hyaline ascospores. Holotype. MFLU 23-0141 Description. Saprobic on Robinia pseudoacacia. Sexual morph: Ascomata 320–470 µm high, 250–600 µm diam. (x – = 396 × 471 µm, n = 5), immersed, with black dots present on host surface or erumpent, visible in bark fissures, scattered, solitary or aggregated in a pseudostroma, perithecial, globose to subglobose, usually unilocular, rarely bilocular, brown to dark brown, coriaceous, ostiolate. Ostiolar neck 90–110 µm wide, papillate, comprising amorphous hyaline cells. Peridium 30–50 µm thick near the apex, 20–35 µm wide at the sides and base, comprising two regions; outer region multi-layered, composed of brown to dark brown, thick-walled cells of textura angularis, fusing and becoming indistinguishable from the pseudostroma or host cells towards the outermost side; inner layer made up of lightly pigmented to hyaline cells merging with the pseudoparaphyses. Pseudoparaphyses 1.5–2.5 µm wide, numerous, filiform, cellular, branched, indistinctly septate, usually guttulate, surrounding the asci and along the innermost layer of the peridium. Asci 80–145 (– 160) × 15–25 µm (x – = 111.5 × 20.9 µm, n = 15), bitunicate, fissitunicate, 8 - spored, hyaline, clavate to cylindric-clavate, straight to slightly curved, thin-walled, short-pedicellate, apically rounded, with an ocular chamber. Ascospores (25 –) 30–40 (– 45) × 6–10 (– 12) µm (x – = 36.8 × 8.6 µm, n = 55), overlapping 1–2 - seriate, hyaline, narrow to broadly fusiform, straight to slightly curved, 1 - euseptate, constricted at the septum, symmetrical or upper cell slightly longer than lower cell, wider upper cell, broad to acute and conically rounded at both ends, smooth-walled, sometimes guttulate, surrounded by a thick or spreading mucilaginous sheath when mature. Asexual morph: Not observed. Culture characteristics. Ascospores germinated on WA within 24 hr. Colony on PDA, reaching 2 cm diam. after 15 days at 25 ° C; above view dark grey in the middle and pale grey edges, dense, circular, umbonate, surface rough, radially furrowed, fimbriate; reverse dark brown, radiating outwardly. Material examined. Italy • Padova, near Torreglia; on dead aerial branches of Robinia pseudoacacia, 18 Nov 2021, E. Camporesi IT 4807 (holotype MFLU 23-0141), ex-type culture MFLUCC 23-0074. Notes. Robiniigena hyalinospora resembles Inflatispora pseudostromatica by its globose to sub-globose ascomata, short-pedicellate asci, and ascospores whose upper cells are comparatively broader than the lower part (Zhang et al. 2011). The ascomata of R. hyalinospora are however, coriaceous and occur in a pseudostroma mainly when they are aggregated, while the ascomata of I. pseudostromatica are hard and form under a black pseudostroma both when the ascomata are solitary or occur in groups (Zhang et al. 2011). Furthermore, R. hyalinospora has narrow to broadly fusiform, 1 - euseptate ascospores with conically rounded ends, whereas I. pseudostromatica comprises narrowly fusiform to nearly cylindrical, 3 - septate ascospores with broadly or narrowly rounded ends (Zhang et al. 2011). Robiniigena hyalinospora is similar to I. caryotae, in terms of 1 - (eu) septate ascospores with a constricted middle septum and surrounded by a mucilaginous sheath (Tibpromma et al. 2017). However, I. caryotae has immersed ascomata while R. hyalinospora has immersed or erumpent ascomata, and the ascospores of I. caryotae are narrowly fusiform with acute ends while those of R. hyalinospora are narrow to broadly fusiform, with comparatively broader and conically rounded ends. Robiniigena hyalinospora, I. caryotae and I. pseudostromatica, are the only taxa in Pleomonodictydaceae with known sexual morphs.