Pyrenothrix nigra Riddle, Bot. Gaz. 64: 513 (1917), Figure 40

= Lichenothrix riddlei Henssen, Ber. dt. bot. Ges. 77: 318 (1964)

= Pleosphaeria lichenothricis Henssen, Ber. dt. bot. Ges. 77: 318 (1964)

MycoBank number: MB 153614;Index Fungorum number: IF 153614; Facesoffungi number: FoF 10392

Thallus corticolous or foliicolous, composed of densely arranged, but not conglutinated, appressed filaments, filaments formed by unbranched or falsely branched photobiont threads wrapped in a sheath of fungal hyphae, hyphae branched and anastomosing, formed by elongate, often strongly curved and terminally inflated, pale brownish cells. Photobiont cyanobacterial. Sexual morph: Ascomata 12–15 mm diam., perithecioid, sessile or immersed between thallus filaments, globose to pear-shaped with a short neck, glabrous. Ostiole indistinct, with rather long, hyaline periphysoids. Excipulum 22–35 μm wide, thin, paraplectenchymatous, composed several layers of narrow to broader, thin-walled to thick-walled and hyaline to strongly pigmented cells. Involucrellum absent. Hamathecium aparaphysate (but empty asci resembling paraphyses often present), gel I+ very faintly bluish, KI+ faintly bluish. Asci 40–55 × 15–25 μm (x̄ = 48 × 20 μm, n = 10), fissitunicate, broadly clavate to saccate, I-, KI- but lumen I+ yellow and KI+ pale yellow (colour of iodine itself). Ascospores 25–34 × 10–12 μm (x̄ = 25 × 8 μm, n = 10),8-spored, uni- or bi-seriate, broadly fusiform, tapering towards both ends, pale to dark grayish brown, transversally septate to muriform, constricted at the septa, thin-walled, without a gelatinous sheath. Asexual morph: Undetermined.

Material examined: USA, Florida, West Palm Beach, on bark of scrub oaks, December 1897, R. Thaxter (FH00259851, holotype).

Figure 40        Pyrenothrix nigra (FH00259851, holotype). a Herbarium material. b Appressed filamentous thallus with perithecia. c Squash mount of ascoma. d Vertical section through ascoma. e Vertical section through peridium. f Ascospores. g, h Asci with ascospores. Scale bars: b = 500 µm, c, d = 50 µm, e, f = 25 µm g =10 µm, h = 5 µm.