Strigula
Strigula Fr., Syst. mycol. (Lundae) 2(2): 535 (1823).
Index Fungorum number: IF 5285; Facesoffungi number: FoF 07706, 30 morphological species (Species Fungorum 2022), 15 species with molecular data.
Lichenized on leaves in terrestrial, lowland to montane, tropical to subtropical, and extending into temperate, habitats. Thallus (pseudo-)corticate, grey-green to bright green, subcuticular and sometimes damaging the supporting leaf. Photobiont Cephaleuros. Sexual morph: Ascomata perithecia, erumpent to prominent, black or covered by thallus layer, lens-shaped to wart-shaped or conical, carbonaceous, ostiolate. Involucrellum present, carbonized. Excipulum prosoplectenchymatous, dark brown to brown black. Hamathecium comprising hyaline, fexuose, unbranched or very rarely branched and anastomosing. Asci usually 8-spored but sometimes 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 uni- or biseriate, fusiform to ellipsoid or bacillar, hyaline, uniseptate, rarely 3-septate, with thin eusepta and rectangular lumina, smooth-walled, often constricted (and sometimes breaking apart) at the septa. Asexual morph: Pycnidia common, immersed to erumpent, visible as black dots, rarely in pseudostromatic clusters, often whole thalli only producing pycnidia. Conidia acrogenous, either macro- or microconidia; macroconidia mostlyuniseptate, ellipsoid to bacillar, with gelatinous appendages, hyaline; microconidia usually aseptate, ellipsoid to fusiform, small, hyaline. Chemistry: No secondary substances known (adapted from Hongsanan et al. 2020b).
Type species: Strigula smaragdula Fr.
Notes: Strigula is characterised by erumpent to prominent, black ascomata, cylindrical to narrowly obclavate asci, and irregularly arranged to uni- or biseriate, fusiform to ellipsoid or bacillary hyaline, uniseptate ascospores. The asexual morph is characterised by immersed to erumpent pycnidia, acrogenous, macro- or microconidia, macroconidia with gelatinous appendages and aseptate, ellipsoid to fusiform, small, hyaline microconidia. Strigula is a heterogeneous genus with three basal lineages differing in morphology comprising S. nitidula, S. prasina group and S. macaronesica. Strigula sensu stricto is characterised by thickened, bright green thalli while S. nitidula group are characterised by thin thalli and S. prasina has hypophyllous thalli with bluish trace and branched and anastomosing paraphyses. Fries (1821) initially cited Strigula as a nomen nudum in his Systema Mycologicum and did not designate a type species. Fries (1823: 535) clearly cited the name Endocarpon smaragdulum. Acharius (1803) initially introduced E. smaragdulum that matches the saxicolous lichen now known as Myriospora smaragdula. Later, Fries (1830) introduced the name Strigula smaragdula which is considered as the established name for the species. Several authors added new species to Strigula sensu lato (Fée 1825, Montagne 1845, Santesson 1952, Hawksworth et al. 1980, Harris 1995, Aptroot et al. 2003, Roux & Sérusiaux 2004, Lücking 2008, McCarthy 2009). Santesson (1952) selected S. smaragdula as the type and this was formally established by Fries seven years later (Fries 1830). Eriksson (1982) and Vézda (1984) accepted only three genera in Strigulaceae namely Strigula, Phylloporis and Raciborskiella. Zahlbruckner (1898) introduced Strigulaceae to accommodate some pyrenocarpus lichens growing on leaves. Members of Strigula associate with photobionts in the genus Cephaleuros (Trentepohliaceae) (Brooks et al. 2015). Harris (1975, 1995) mentioned that the ecological differences are not reliable for generic delineation. With time, several authors broadened the generic concept of Strigula sensu lato to include corticolous and saxicolous species (Hawksworth et al. 1980, McCarthy 1995, Roux & Sérusiaux 2004). Strigula jamesii is the only non-foliicolous species that has sequence data and was initially described in Geisleria and later transferred to Strigula (Hawksworth et al. 1980). Harris (1995) suggested to synonymize Phyllobathelium with Strigula but other authors did not agree and considered these two genera as distinct (Aptroot et al. 1997, Lücking 2008, McCarthy 2009). Around 30 completely foliicolous species are included in Strigula sensu stricto (Jiang et al. 2020). Harris (1995) wrongly mentioned Shanoria as a synonym of Strigula and introduced S. indica that characterizes the pycnidial stage of Strigula cf. nitidula but Anahosur (1967) did not introduce a new genus but rather accommodated its new species in the existing genus, Shanoria typifed by S. bambusarum (Subramanian & Ramakrishnan 1956). The name Shanoria Anahosur does not exist as the latter is now a synonym of Placonema (Sacc. & D. Sacc.) Petr. Phylogenetic analyses demonstrated that Strigula smaragdula is a collective species with the type species described from Nepal (Oh et al. 2019, Woo et al. 2020, Jiang et al. 2020). Morphological species recognition is not reliable to distinguish among species of Strigula due to intra-specific variation of thallus morphology and phylogenetic analysis of molecular data can provide better delimitation of Strigula species and unravel cryptic diversity. Lücking (2008) provided a comprehensive modern account of the foliicolous taxa in his monograph for Flora Neotropica. Moon and Aptroot (2009) identified three other species S. melanobapha, S. nemathora and S. subelegans based only on morphology. Jiang et al. (2016, 2017a, b) reported numerous new species of Strigula morphologically similar to S. antillarum, S. nitidula and S. smaragdula based on phylogenetic analyses of ITS sequence data. Jayalal et al. (2013) added four foliicolous lichen species, S. concreta, S. macrocarpa, S. melanobapha, and S. subelegans from South Korea based on morphology and molecular study of ITS sequence data. Aptroot et al. (2014) showed that G. sychnogonoides, the type species of Geisleria is not related to Strigulaceae but is close to members of Stictidaceae. Woo et al. (2020) reported two new foliicolous species, S. depressa and S. multiformis based on morphological and anatomical characters namely phorophyte-dependent variation of thallus morphology. Strigula is a distinct and type genus of Strigulaceae. Molecular markers available for Strigula include ITS, SSU, LSU, TEF-1 and RPB2.
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