Ostreola Darker, Can. J. Bot. 41: 1383 (1963).
Index Fungorum number: IF 3648; Facesoffungi number: FoF 08104, 8 morphological species (Species Fungorum 2021), molecular data unavailable.
Saprobic on host. Sexual morph: Hysterothecia mostly crowded, scattered or in groups, conchiform to hatchet shaped, occasionally triradiate, slightly crested, fragile, opening narrowly by a longitudinal slit, shining black, umbonate, with concentric striae, at base abruptly narrowing to a rounded or elliptical attachment with the substratum; hysterothecia in transverse section with covering layer of dark pseudoparenchyma with apex abruptly tapering to the more or less closed lips, brown basal pseudoparenchyma, often continued into the substratum as a foot-like structure; hypothecium of thin walled pseudoparenchymatous cells; hymenium flat, asci cylindrical, eight-spored; paraphyses simple or branched, equaling or slightly longer than the asci; ascospores uniseriate, obovate, transversely 3-5(-7)-septate, slightly constricted in the middle, muriform, with (1-)2-3(-7) longitudinal septa, dull yellow-brown with brown walls and septa. Asexual morph: Unknown (Adapted from Darker 1963).
Type species: Ostreola consociata Darker
Notes: Ostreola was introduced by Darker (1963) with O. consociata as type species. Ostreola is characterized by conchiform to hatchet shaped hysterothecia opening narrowly by a longitudinal slit, cylindrical, eight-spored asci and obovate, transversely 3-5(-7)-septate ascospores. Ostreola resembles Mytilinidion in having dictyospored ascospores. Ostreola also resemble Ostreichnion in having muriform ascospores but can be differentiated in that the former has smaller ascospores (Barr 1990). Tilak and Kale (1968) added two other species from India, viz. O. indica and O. ziziphi, both from non-coniferous substrates. Ostreola is currently a distinct genus in Mytilinidiaceae but molecular data is lacking hence fresh collections are needed to confirm the natural placement of the genus.