Raciborskiella
Raciborskiella Höhn., Sber. Akad. Wiss. Wien, Math. -naturw. Kl., Abt. 1 118: 1176 (1909).
Index Fungorum number: IF 4636; Facesoffungi number: FoF 08887, 2 morphological species (Species Fungorum 2022), 2 species with molecular data.
Thallus foliicolous, subcuticular, hypophyllous, dispersed into rounded, partly confluent patches with entire margins, very thin, usually dark bluish grey. Photobiont Cephaleuros. Sexual morph: Perithecia fully exposed, prominent, more or less conical, not covered by thallus, black; excipulum prosoplectenchymatous, colorless; involucrellum carbonized, black; hamathecium colorless, I–, KI–; paraphyses slightly branched and anastomosing. Asci bitunicate, with short tholus and narrow ocular chamber, I–, KI–, clavate to oblong. Ascospores 8 per ascus, 2-seriateto irregular arranged, fusiform, uniseptate, colorless, rather large, strongly constricted at the septum and frequently breaking into part spores, both ends sometimes with thin, gelatinous appendages. Asexual morph: Pycnidia adnate, wart-shaped to conical, black. Macroconidia bacillar to filiform, uniseptate, colorless, both ends with short to medium-sized, gelatinous appendages (not exceeding 50 μm even after prolonged time in squash mounts). Microconidia fusiform-ellipsoid, non-septate, colorless. Chemistry: No substances detected by TLC (adapted from Jiang et al. 2020).
Type species: Raciborskiella talaumae (Racib.) Höhn.
Notes: Raciborskiella is characterised by prominent, more or less conical perithecia, clavate to oblong asci and fusiform, uniseptate, colorless ascospores. The asexual morph is characterised by adnate, wart-shaped to conical, black pycnidia, bacillar to filiform, uniseptate macroconidia and fusiform-ellipsoid, non-septate, colorless microconidia. Raciborskiella differs from Phylloporis in growing entirely on the leaf underside while members of Phylloporis (previously known as Porina) are supracuticular (Santesson 1952, Vézda 1984). Santesson (1952) accepted two species and treated Raciborskiella as a distinct genus and this was followed by several authors (Singh 1970, Vézda 1984, Roux & Sérusiaux 1995, Sérusiaux & Polly 1996). Harris (1995), Lücking (2008) and McCarthy (2009) did not agree with Santesson (1952) and included Raciborskiella within Strigula sensu lato. Santesson (1952) also considered Clypeolum talaumae and Melanopsamma areolatum as synonyms of Raciborskiella janeirensis though the former genera have smaller ascospores. Raciborskiella janeirensis sensu Santesson (1952) comprises two phylogenetically distinct species namely R. janeirensis sensu stricto and R. talaumae, the type of the genus, which also have different ascospores size. Jiang et al. (2020) resurrected Raciborskiella based on multigene analyses of SSU, LSU, TEF1-α and RPB2 and unique morphology namely thin, bluish grey thallus, branched and anastomosing paraphyses, large and strongly constricted ascospores at times with thin appendages. Jiang et al. (2020) also revised the type specimen and reinstated Clypeolum talaumae as Raciborskiella talaumae based on the smaller ascospores. Jiang et al. (2020) showed that the two accepted species of Santesson (1952) are not closely related as Strigula prasina clustered within Strigula s. str.in the multigene analyses of SSU, LSU, TEF1-α and RPB2. The authors also mentioned that the hypophyllous growth is not a diagnostic character for Raciborskiella. Raciborskiella differs from Strigula sensu stricto in having large ascospores, up to three to four times longer. The term ‘Raciborskiella Speg.’, a supposedly illegitimate later homonym of Raciborskiella Höhn. is not valid and hence, the name ‘Raciborskiella Höhn’ is recognized. Raciborskiella differs from Phylloporis in growing entirely on the leaf underside while members of Phylloporis (previously known as Porina) are supracuticular (Santesson 1952, Vézda 1984). Raciborskiella is morphologically and phylogenetically a distinct genus in Strigulaceae. Molecular markers available for Raciborskiella talaumae are ITS, SSU, TEF-1 and for R. janeirensis include ITS, SSU and TEF-1.
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