Placocrea Syd., Annls mycol. 37(4/5): 380 (1939).
Index Fungorum number: IF 4124; Facesoffungi number: FoF 06944, 1 morphological species (Species Fungorum 2022), no molecular data available.
Parasitic associated with living leaves. Sexual morph: Ascostromata superficial, easily removed from the host surface, orange brown to black, flattened to slightly raised, pad-like, circular to undulate, or orbicular, yellowish to orange around the ascostromata, gregarious or solitary, fleshy, soft when rehydrated by water, easily cracking when dry, stromatal structure composed of palisade- to globular, orangish cells. Ascomata semi-immersed to superficial, orange yellowish to orange-brown, globose to subglobose, or ovoid, soft and fleshy, scattered, gregarious, with apical ostiole, with thick, septate, hairy ostiole, surrounded by loose, hyphae. Peridium comprising 4–7 layers of orange-yellowish, pseudoparenchymatous cells, arranged in a textura angularis to prismatica. Hamathecium comprising dense, anastomosed, cellular pseudoparaphyses branched at the apex. Asci 8-spored, bitunicate, fissitunicate, cylindrical to cylindric-clavate or ampulliform, subsessile, apex rounded, with an indistinct ocular chamber. Ascospores overlapping 2–3-seriate, hyaline to subhyaline, becoming pale yellowish in mass, oblong to fusiform, uniseptate, upper cell larger than lower cell. Asexual morph: Unknown (adapted from Boonmee et al. 2017).
Type species – Placocrea pulchella Syd.
Notes – Placocrea is characterised by superficial, flattened to slightly raised, gregarious or solitary ascostromata, semi-immersed to superficial globose to subglobose ascomata, peridium comprising pseudoparenchymatous cells, arranged in a textura angularis to prismatica, fissitunicate, cylindrical to cylindric-clavate asci and hyaline to subhyaline ascospores which become pale yellow on maturity (Sydow & Sydow 1939). Sydow and Sydow (1939) referred Placocrea as closely related to Nectria based on the structure of the ascomata. Petrak (1952) re-described Placocrea and transferred the genus to Mycosphaerellaceae based on the morphological resemblance with Mycosphaerella. This taxonomic treatment was followed by several authors (Arx & Müller 1975, Kirk et al. 2001, 2008, Lumbsch & Huhndorf 2007, 2010, Hyde et al. 2013, Wijayawardene et al. 2014). Hyde et al. (2013) reported that the placement of Placocrea in Mycosphaerellaceae was doubtful. Boonmee et al. (2017) re-examined the type specimens of Placocrea pulchella from BPI and S herbaria and reported that Placocrea was different based on the presence of pseudoparaphyses while other genera in Mycosphaerellaceae lacked pseudoparaphyses. The authors transferred Placocrea to Teratosphaeriaceae based on the parasitic lifestyle and anastomosing pseudoparaphyses (Hyde et al. 2013). Currently, Placocrea is accommodated in Teratosphaeriaceae but DNA sequence data is needed to confirm this taxonomic placement.
Species