Stemphylium Wallr., Fl. crypt. Germ. (Norimbergae) 2: 300 (1833).
Index Fungorum number: IF 10081; Facesoffungi number: FoF 07388, 99 morphological species (Species Fungorum 2022), 31 species with molecular data.
Saprobic or pathogenic on host. Sexual morph: Ascomata black, solitary, immersed to erumpent, base not easy to remove from the substrate, subglobose to ampulliform, coriaceous, with flattened ostiole. Ostiole minute papillate, smooth, ostiolar canal filled with hyaline cells. Peridium usually composed with two layers, thick at the sides and thinner at the base, outer layer of heavily pigmented thick-walled cells of textura angularis, inner layer composed of hyaline to pale brown, thin-walled cells of textura angularis. Hamathecium of cellular, septate, broad, dense pseudoparaphyses. Asci 8-spored, bitunicate, fissitunicate, broadly cylindrical to cylindric-clavate, with a short pedicel and a minute ocular chamber. Ascospores uni- to bi-seriate, partially overlapping, pale brown to brown, mostly ellipsoidal, muriform with 4–7 transverse septa and 1–3 longitudinal septa, sectored, with a sheath (Adapted from Brahamanage et al. 2017) Asexual morph: Conidiophores solitary, straight to flexuous, occasionally branched, septate, smooth, pale brown, bearing 1–3 darkened percurrent rejuvenation sites. Conidiogenous cells swollen at the apex, darkened. Conidia solitary, conidium body pale olivebrown, verrucose, ellipsoid to cylindrical with 2–4 transverse septa and 1–3 longitudinal and 0–2 oblique septa per transverse sector. Constricted at 1–2 darkened transverse septa (Adapted from Crous et al. 2016).
Type species: Stemphylium botryosum Wallr.
Notes: Stemphylium was introduced by Wallr (1833) with S. botryosum as type species. Stemphylium is characterized by black, solitary, immersed to erumpent ascomata, broadly cylindrical to cylindric-clavate asci and pale brown to brown, ellipsoidal, muriform with 4–7 transverse septa and 1–3 longitudinal septa and a sheath. Stemphylium is a dematiaceous genus, which differs from other hyphomycetes in having phaeodictyospores, percurrent rejuvenation of the conidiophores, and apically swollen conidiogenous cells while other closely related genera such as Alternaria has geniculate, sympodial proliferation (Camara et al. 2002; Inderbitzin et al. 2009; Woudenberg et al. 2017). The sexual morph to which Stemphylium is linked is Pleospora sensu stricto (Inderbitzin et al. 2009; Woudenberg et al. 2017). Chaisrisook et al. (1995) studied the molecular genetic relationship of five Stemphylium species pathogenic to alfalfa but considered five species to be distinct based on RAPD fingerprints, morphology and ecology studies which according to the multigene phylogeny should be synonymized. Câmara et al. (2002) provided a phylogenetic tree from ITS and GAPDH of 16 species of Stemphylium and pointed out that the morphological diagnostic characters of Stemphylium are size and shape of conidia, conidiophores, ascospores, and size and time of growth of pseudothecia while other characters such as septum development and small variations in conidial wall ornamentation are not as useful. Inderbitzin et al. (2009) gave an account of the Pleospora species with Stemphylium asexual morphs but several species were unspecified indicating the problems in identification of Stemphylium taxa. Rossman et al. (2015) recommended the use of Stemphylium over Pleospora based on one fungus-one name rule and this has been followed by several authors (Hongsanan et al. 2017; Wijayawardene et al. 2018, 2020). Woudenberg et al. (2017) reported that name changes in these Stemphylium is necessary according to one fungus-one name initiative and this required further studies. Brahmanage et al. (2018) gave an overview on the pathogenicity, disease severity, distribution and molecular phylogenetic affinities of pathogenic isolates of Stemphylium. Over the past decade, several species have been added to Stemphylium (Wang and Zhang 2006, 2009; Wang et al. 2009, 2010; Pei et al. 2009, 2010, 2011; Yan-Fang et al. 2012; Deng et al. 2014; Crous et al. 2016; Brahamanage et al. 2019; Phukhamsakda et al. 2020). Several phylogenetic studies based on ITS, mtSSU, TEF-1, intergenic spacer between vmaA and vpsA, GAPDH have been carried out by different authors to delimit species in Stemphylium (Câmara et al. 2002; Pryor and Bigelow 2003; Kodsueb et al. 2006; Inderbitzin et al. 2009) but in some cases, sequence data were not reliable to differentiate species which were morphologically different (Inderbitzin et al. 2009; Pei et al. 2011). Sharma et al. (2020b) reported on the genome resource for two S. vesicarium isolates causing Stemphylium leaf blight of onion in New York. Stemphylium is a well-defined monophyletic genus in the family Pleosporaceae. But since the sexual morph to which Stemphylium is linked, Pleospora is polyphyletic, several species lacking molecular data might not belong to Stemphylium. Molecular data available for Stemphylium include LSU, SSU, ITS, TEF-1, RPB2, CAL, GAPDH and β-tubulin. The recommended genetic marker at genus level is ITS and for species level is CAL and GAPDH (Crous et al. 2016).