Rhytidhysteron tectonae Doilom & K.D. Hyde, sp. nov. Index Fungorum number: IF551964

Etymology: Name refers to the host genus Tectona on which the fungus was collected.

Holotype: MFLU 15–3207

Saprobic on dead branches of T. grandis. Sexual morph: Ascomata 1225–3365 μm long × (370–)574–705(−835) μm high × (325 – )550 – 640( − 728) μ m wide ( x = 2175 × 585 × 523μm, n= 30), hysterothecial with a longitudinal slit, black, solitary to aggregated, semi-immersed to superficial, subiculum, coriaceous, smooth without striation, yellow at the center, when dry folded at the margin, forming an elongate slit. Exciple 80–135μm, (x = 100, n= 20), composed of a textura angularis, comprising of two cell layers, outer layer comprising black to dark reddish, thick-walled cells, inner layer comprising hyaline, thin-walled cells. Hamathecium comprising 1.2–2μm wide, dense, septate, pseudoparaphyses, filiform, forming epithecium above the asci and enclosed in a gelatinous matrix. Asci (135–)150–160(−176) × 10–15 μm (x = 155 × 13μm, n= 15), 8-spored, bitunicate, subcylindrical to cylindrical, with a short furcate pedicel, apically rounded, sometimes without a distinct ocular chamber. Ascospores (19–)28–29(−31) × (8–)10–12(−13) μm (x = 27 × 10μm, n= 30), uni-seriate, slightly overlapping, initially subglobose and 1-septate, hyaline to pale brown, becoming pale brown to dark brown with 2–3-septa, ellipsoidal to fusiform, slightly rounded or pointed at both ends, constricted at the central septum, without a mucilaginous sheath. Asexual morph: Undetermined.

Culture characteristics: Ascospores germinating on PDA within 24 h. Germ tubes produced at both end of ascospores. Colonies on MEA reaching 25–30 mm diam. after 7 days in the dark at 25 °C (x = 28, n= 5), fimbriate, fluffy, convex with papillate surface, aerial, dense, white (5A1) at the edge, grey (5C1) at the center from above, golden brown (5D6) at the edge and greyish orange (5B3) at the center from below.

Habitat: Known to inhabit dead branches of T. grandis (current study).

Known distribution: Thailand (current study).

Material examined: THAILAND, Chiang Rai Province, Muang District, on dead branches of T. grandis, 18 July 2013, R. Phookamsak, (MFLU 15–3207, holotype), ex-type living culture MFLUCC 13–0710, MKT 156, ICMP 21175, GenBank Accession No: ITS: KU144936, LSU: KU764698, SSU: KU712457, TEF1: KU872760.

Notes: Rhytidhysteron tectonae is introduced as a new species based on multi-gene phylogenetic analysis and morphological differences from known Rhytidhysteron species according to the recent key for Rhytidhysteron in Thambugala et al. (2016). Rhytidhysteron tectonae is distinguished from R. neorufulum in possessing a coriaceous, two-layered exciple, and semi-immersed to superficial ascomata, while that of R. neorufulum is carbonaceous, one-layered and superficial. The ascospores of R. tectonae are shorter and wider than R. neorufulum (27 × 10 versus 31.2 × 8.9 μm) as reported in Thambugala et al. (2016) for the holotype.

FIG Rhytidhysteron tectonae (MFLU 15–3207, holotype). a, b Hysterothecia on host surface. c,d Vertical section through hysterothecium. e Pseudoparaphyses. f Exciple. g, h Asci with ascospores and pseudoparaphyses. i Subiculum of hysterothecium. j Immature ascospore with 1-septum. k Ascospore becoming mature and 1-septate. l Mature ascospore with 3-septa. m Germinated mature ascospore. Notes: e, f Stained in lactophenol cotton blue. Scale bars: a, b = 1000 μm, c, d = 100 μm, e–h, m = 10 μm, i = 20 μm. j–l = 5 μm