Raciborskiella Höhnel, Sitz.ber. Math.-Nat. Kl. Akad. Wiss. Wien, Ser. 1, 118: 1176 (1909); Santesson, Symb. Bot. Upsal. 12(1): 194 (1952); Jiang et al., Fungal Div. 102: 278.
MycoBank number: MB 4636; Index Fungorum number: IF 4636; Facesoffungi number: FoF 08887; two morphologically and phylogenetically delimited species (Jiang et al. 2020b).
Lichenized on the underside of leaves in terrestrial, lowland to montane, tropical habitats. Thallus (pseudo-) corticate, greenish to bluish grey, subcuticular. Photobiont Cephaleuros. Sexual morph: Ascomata perithecia, prominent, black, conical, carbonaceous, ostiolate. Involucrellum present, carbonized. Excipulum prosoplectenchymatous, dark brown to brown-black. Hamathecium comprising 0.5–0.7 µm wide paraphyses, hyaline, flexuose, unbranched or very rarely branched and anastomosing. Asci 8-spored but appearing 9–16-spored due to ascospores breaking in halves within the asci, bitunicate, fissitunicate, cylindrical to narrowly obclavate, shortly pedicellate, with narrow ocular chamber, non-amyloid. Ascospores irregularly arranged to biseriate, fusiform, hyaline, 1-septate, with thin eusepta and rectangular lumina, smooth-walled, strongly constricted and breaking apart at the septa, comparatively large (over 30 µm and up to 70 µm long). Asexual morph: Pycnidia common, erumpent, visible as black dots. Conidia acrogenous, either macro- or microconidia; macroconidia 1-septate, bacillar, with gelatinous appendages, hyaline; microconidia usually aseptate, ellipsoid to fusiform, small, hyaline.
Chemistry: No secondary substances known.
Type species: Raciborskiella talaumae (Racib.) Höhn., Sber. Akad. Wiss. Wien, Math.-naturw. Kl., Abt. 1 118: 1176 (1909).
Notes: This genus was kept separate by Santesson (1952), on account of the hypophyllous growth and the branched and anastomosing paraphyses particularly in Raciborskiella janeirensis. However, molecular data demonstrate that R. prasina, which differs considerably from R. janeirensis in morphology and anatomy, is unrelated to the latter and belongs in the genus currently recognized as Strigula sensu stricto above. As a result, the most distinctive character of Raciborskiella are the unusually large ascospores, up to three to four times longer that in species of Strigula sensu stricto.