Karstenula
Karstenula Speg., Decades Mycologicae Italicae 7–12: no. 94 (in sched.) (1879).
Index Fungorum number: IF 2549; Facesoffungi number: FoF 00042, 22 morphological species (Species Fungorum 2022), 1 species with molecular data.
Saprobic on dead wood and stems in terrestrial habitats. Sexual morph: Ascomata rarely small, usually medium-sized, immersed usually under thin clypeus, scattered to gregarious, with flattened top and rounded pore-like ostiole, coriaceous. Peridium 2-layered, outer layer composed of reddish-brown to dark brown small cells, with inner layer of pale compressed cells. Hamathecium of dense, cellular pseudoparaphyses. Asci bitunicate, fissitunicate, cylindrical to cylindro-clavate with short furcate pedicel. Ascospores ellipsoid to fusoid, reddish-brown to dark brown muriform. Asexual morph: Microdiplodia (adapted from Constantinescu 1993, Ariyawansa et al. 2014).
Type species: Karstenula rhodostoma (Alb. & Schwein.) Speg.
Notes: Karstenula is characterised by medium-sized ascomata, immersed under thin clypeus, cylindrical to cylindro-clavate asci and ellipsoid to fusoid, reddish-brown to dark brown, muriform ascospores. Karstenula has been synonymized under Pleomassaria by several authors (Lindau 1897, Winter 1885). Karstenula resembles Didymosphaeria in having ascomata held in a subiculum or below a clypeal thickening and at times apical cells turn reddish or orange-brown (Barr 1990). Barr (1990) revised the concept of Karstenula sensu lato, which includes some taxa of Thyridium and treated Karstenula as having trabeculate pseudoparaphyses, however Karstenula has cellular pseudoparaphyses. Karstenula resembles Byssosphaeria and Herpotrichia in having similar ascomata that are pale-coloured near the ostiole with similar peridium structure developing under a subiculum. Karstenula also resembles Herpotrichia in having cellular pseudoparaphyses and cylindrical asci. Karstenula differs from Byssosphaeria and Herpotrichia in having 3-septate ascospores with the rare longitudinal septum while those of the latter two genera areuniseptate. In the phylogenetic analysis of Kodsueb et al. (2006) and Zhang et al. (2009), Karstenula rhodostoma (CBS 690.94) forms a strong lineage with Phaeodothis winteri, Didymocrea sadasivanii, Bimuria novae-zelandiae and some taxa of Letendraea and Paraphaeosphaeri. Zhang et al. (2012) tentatively included Karstenula in Montagnulaceae based on phylogenetic evidence. In the phylogenetic analysis of Ariyawansa et al. (2014), putative strain of Karstenula rhodostoma (CBS 690.94) clustered in Didymosphaeriaceae, sister to the Paraphaeosphaeria clade and hence was tentatively referred to Didymosphaeriaceae. Karstenula is currently a distinct genus in Didymosphaeriaceae but more collections with sequence data are needed to confirm the taxonomic placement of the genus. The type must be re-collected and sequenced. Molecular markers available for Karstenula are ITS, LSU, SSU, RPB2 and TEF-1.
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