Isothea rhytismoides  

Infected areas 1-2.5 mm diam., the included leaf tissue sometimes reddish brown.
Anamorph: not known.
Teleomorph: stromata hologenous (though usually not visible from the lower surface due to the leaf tomentum), the ostioles epigenous. Blackened tissue sometimes spreading between ascomata below the cuticle but much more heavily developed above and below ascomata (in roughly circular regions 120-200 μm diam.), restricted to an upper and lower layer, subcuticular, composed of heavily melanized epidermal and some palisade cells, fungal tissue not clearly visible, eventually covering almost the whole of the infected area. Ascomata usually strongly aggregated, clearly distinguishable from the surface even in old colonies, from the surface usually strongly domed, the ostiole inconspicuous; 200-320 μm diam., usually slightly oblate; peridium 8-14 μm thick, composed of 4-5 layers of strongly compressed hyaline pseudoparenchymatous cells with walls to nearly 1 μm thick, sometimes apparently merging with compressed host tissue at the sides of the ascomata, in the ostiolar region forming swollen and pigmented clavate periphysis-like elements with cells to 18 x 4 μm, merging into true hyaline periphyses within. Centrum formed from a thin layer of very thin-walled pseudoparenchymatous tissue lining the lower part of the wall. Interascal tissue of inconspicuous paraphyses, formed (sometimes in pairs) from +globose cells and with at least the lower septa often constricted, to 8 μm diam., gradually tapering, very thin-walled, about as long as the asci. Asci 67-95 x 16-22.5 μm, clavate, short- to long-stalked (occasionally to ca 40 μm), swelling significantly just before ascospore release, thin-walled at all stages, the apex obtuse to rounded, with a small sometimes inconspicuous apical ring ca 4 μm diam. and 0.5 μm thick, usually 8-spored but ascospores frequently aborting. Ascospores arranged irregularly, (9.5-)12.5-16 x 5-6.5 μm, usually ± cylindrical with round ends, sometimes cylindric-ellipsoidal or ovoid, often slightly larger and/or irregularly shaped in asci with fewer than 8 ascospores; thin- and smooth-walled, aseptate, often strongly guttulate, without a gelatinous sheath. Appressoria to 7 μm long, widely clavate,  mid brown, formed directly from germinating ascospores, occasionally while still in the ascoma.