Asterina
Asterina Lév., Annls Sci. Nat., Bot., sér. 3 3: 59 (1845).
Index Fungorum number: IF 409; Facesoffungi number: FoF 06727, >1000 morphological species (Species Fungorum 2022), 9 species with molecular data.
Epiphytes obligately biotrophic on leaves, forming blackened, circular, elgonate or X- or Y-shaped areas. Superficial hyphae spreading over the leaf surface, with appressoria or sometimes absent, scattered with superficial thyriothecia. Appressoria circular, lateral and alternative, sparsely septate, penetrating the host cells with haustoria. Sexual morph: Thyriothecia solitary, gregarious, superficial, developed below or somtimes lateral on surface of hyphae, easily removed from the host surface, rounded, black, dehiscing to open by slit-like, star-like, or X- or Y-shaped fissures when mature. Upper wall comprising a thin layer of mostly neatly arranged dark cells, which are branched at the outer rim, from which hyphae strands develop, base poorly developed. Hamathecium usually lacking pseudoparaphyses. Asci 8-spored, bitunicate, fissitunicate dehiscence not observed, oblong to subglobose, lacking a pedicel, apical region of asci usually with a thick opaque region, ocular chamber not observed, not staining blue in IKI, asci arranged vertically in the thyriothecium. Ascospores overlapping, conglobate, hyaline when immature, usually brown when mature, uniseptate, strongly constricted at the septum. Asexual morph: “Asterostomella”, “Clasterosporium”-like, “Mahanteshamyces”. Superficial hyphae brown, with appressoria. Conidiomata pycnothyria flattened, dimidiate, radiate, orbicular, stellately dehisced at the centre. Conidia brown, ovate, pyriform, angular, or wall straight to sinuate (adapted from Hyde et al. 2013, Hongsanan et al. 2014).
Type species: Asterina melastomatis Lév.
Notes: Asterina is characterised by circular, lateral and alternative appressoria, solitary, gregarious, superficial thyriothecia, with stellate dehiscence, oblong to subglobose asci and overlapping, conglobate, 1-septate and hyaline to brown ascospores. The asexual morph is “Asterostomella”, “Clasterosporium”-like, or “Mahanteshamyces”, characterised by flattened pycnothyria and brown, ovate, pyriform, angular conidia but these are not linked by cultural or molecular data. The holotype material of Léveillé’s specimen is lost. Theissen (1912a) chose A. azarae Lév. as the neotype since the identity of the specimen observed by Montagne and Léveillé were at no time authenticated. Theissen (1912a) deposited this specimen in P herbarium with a precise description and illustration. Subsequent authors did not follow Theissen’s suggestions and considered A. melastomatis as the type species. Several authors described numerous Asterina species (Spegazzini 1888, Rehm 1901, Sydow 1929, Firmino et al. 2019) hence, the concept of the genus became heterogeneous and comprised taxa with dimidiate and globose thyriothecia. Theissen (1913) first provided a monograph of Asterina based on 343 described species and transferred 261 species to other genera. Introduction of new species, combinations together with the 82 species left in 108 species in Asterina (Theissen 1913). Around 130 new Asterina species were described between 1911 and 1939 but most lacked illustration and were not fully justified (Index Fungorum 2022). Asterina presently comprises more than 1000 species (Hosagoudar & Abraham 2000, Hongsanan et al. 2020b). Asterina is the largest genus within Asterinaceae. Sivanesan (1984) demonstrated the link of Asterostomella clasterosporium with “Clasterosporium”- like morphs but this was doubtful because it was not certain whether the two fungi occur together or they are just hyper parasitic. Sivanesan (1984) also reported that several Asterina species are linked with Asterostomella pycnidial states. Arx and Müller (1975), Hosagoudar (2010) and Hofmann (2013) also linked Asterostomella with Asterina. Hyde et al. (2013) synonymized Asterostomella with the older name Asterina since A. paraguayensis forms thyriothecia on living leaves. Hyde et al. (2013) reported an “Asterostomella”-like state associated with Caryospora. Hyde et al. (2013) also considered Mahanteshamyces as a synonym of Asterina as it is an asexual state of Asterina. Hosagoudar et al. (2002, 2004, 2007, 2009, 2012) provided several publications on Asterina and similar genera such as Bheemamyces, Gangamyces, and Ishwaramyces. It is difficult to re-study these genera and confirm the characters since the herbarium specimen are deposited in HCIO and TBGT, which will not loan specimen outside India. Hence, most of the published results cannot be re-assessed and it is better to have sequence data for these genera to check whether the morphological differences are taxonomically significant at the molecular level. Hongsanan et al. (2014) treated the genera Bheemamyces, Gangamyces and Ishwaromyces as doubtful and synonymized them with Asterina until fresh collections are obtained. Asterina is morphologically and phylogenetically a distinct and type genus of Asterinaceae but requires revision as it is assorted with various species lacking sequence data. Molecular markers available for Asterina are ITS, LSU and SSU.
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