Placostromella
Placostromella Petr., Sydowia 1(1–3): 9 (1947).
Index Fungorum number: IF 4141; Facesoffungi number: FoF 08119, 3 morphological species (Species Fungorum 2022), no molecular data available.
Epiphytic on living leaves. Sexual morph: Ascostromata subcuticular, carbonaceous, loosely scattered, black, rounded or broadly ellipsoid, sometimes coalescent, uniloculate and opening when wet by irregular or longitudinal splits. Upper wall consisting of several rows of irregularly arranged, dark brown, angular cells. Lower wall brown to dark brown, sometimes absent, with irregular to ± angular cells. Peridium base poorly developed, comprising a single substratum of several layers of compressed dark brown-walled cells of textura angularis. Hamathecium of colourless, smooth, septate, thin-walled, filiform pseudoparaphyses, branching dichotomously at acute angles. Asci 8-spored, bitunicate, cylindrical to clavate, subsessile or short pedicellate with broadly rounded ends. Ascospores overlapping, 1–3-seriate, hyaline, sometimes becoming light brown to brown, cylindric-ellipsoidal or oblong to obovate with broadly rounded ends with a thin gelatinous sheath, verrucose, uniseptate, the upper cell often broader than the lower one, more or less constricted at the septum. Asexual morph: Unknown (adapted from Inácio et al. 2005, Thambugala et al. 2014).
Type species: Placostromella macrospora Petr.
Notes: Placostromella is characterised by subcuticular, carbonaceous ascostromata, cylindrical to clavate, subsessile or short pedicellate asci, cylindric-ellipsoidal or oblong to obovate ascospores with broadly rounded ends and a thin gelatinous sheath. Batista and Maia (1964) added P. amazonensis. Palawaniella castanopsis resembles members of Placostromella in having subcuticular, black, shiny ascomata with a definite margin, colorless, smooth, septate, thin-walled, filiform interthecial filaments, clavate to cylindric-clavate or broadly clavate asci anduniseptate ascospores surrounded by a gelatinous sheath (Kapoor 1968, Inácio et al. 2005). Eriksson (1984), Hawksworth et al. (1995) and Kirk et al. (2001) treated Placostromella in Dothideales. Eriksson et al. (2003) and Lumbsch and Huhndorf (2010) listed Placostromella under Dothideomycetes, genera incertae sedis. Inácio et al. (2005) transferred Palawaniella castanopsis to Placostromella castanopsis. Inácio et al. (2005) suggested the placement of Placostromella in Parmulariaceae based on the form and position of the internal stroma and structure of the ascomata and excluded it from the Dothideales based on the occurrence of interthecial filaments. Thambugala et al. (2014) re-examined the holotype specimen of P. macrospora from W but did not find any interthecial filaments. Thambugala et al. (2014) tentatively placed Placostromella in Parmulariaceae. Placostromella is a distinct genus in Parmulariaceae. Molecular data is lacking. Fresh collections with DNA sequence data are needed to confirm the taxonomic placement of the genus.
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