Keissleriella ocellata, Keissleriella ocellata
Anamorph: not known.
Teleomorph: ascostromata perithecial, 150-210 x 140-180 µm, oblate to shallowly conical, formed in clusters of 3-6 below clypeus-like blackened and shallowly domed epidermal tissue, the ostiole distinctly papillate. Peridium 15-30 µm thick, composed of 4-5 layers of thick-walled dark brown angular cells 4-12 µm diam., in the basal region thinner and less strongly pigmented. Ostiole lined with thin-walled hyaline periphysis-like cells 10-15 µm long and ca 2 µm diam. Interascal tissue composed of wide thin-walled cellular pseudoparaphyses 2-3 µm diam. Asci 67-97 x 10-13 µm, cylindrical to cylindric-clavate, mostly short-stalked, the apex rounded, thick-walled and fissitunicate with a clear ocular chamber, 8-spored. Ascospores arranged biseriately or obliquely uniseriately, 15-18.5 x 5.5-6.5 µm [14-22 x 6-7 µm fide Bose 1961], cylindric-fusiform, 2-septate with the middle cell noticeably swollen, constricted especially at the primary (lower) septum, hyaline, thin-walled, smooth, with a mucous sheath ca 1 µm thick that is evanescent at maturity of the spore.
Not formally assessed. There are 13 records in FRDBI that are widely distributed, and bearing in mind the species is inconspicuous it may well be common but overlooked. However, it does appear to be host-specific.
Easily distinguished from other species of Keissleriella by its 2-septate ascospores (a very unusual attribute for the Ascomycota as a whole), its hyaline periphysis-like ostiolar hairs and its ascomata that are clustered under a common clypeus-like structure. The species may not be congeneric with Keissleriella, but an alternative placement has not been found.
Apparently confined to dead attached (upright) stems of Hypericum perforatum, with a single report from H. maculatum.
Scattered throughout England with records from Norfolk, Shropshire, Surrey, Wiltshire and MW Yorkshire, and Wales (Pembrokeshire).