Anamorph: Sphaerellopsis filum; a microconidial anamorph also exists. Conidiomata immersed within stromatic tissues but sometimes becoming erumpent, unilocular or multilocular, the locules then almost superficial and appearing pycnidial, ostiolate, the wall composed of dark brown thick-walled textura angularis. Conidiophores formed from the inner cells of the conidiomatal wall, poorly differentiated, sometimes branched at the base, hyaline to pale brown. Conidiogenous cells 7.5-20 x 5-7 µm, doliiform to cylindrical, often with 1-3 percurrent and/or annellidic proliferations. Conidia 17-20 x 5.5-6.5 µm, ellipsoidal, often with one median septum, not constricted at the septum, the apex obtuse and the base truncate, smooth and hyaline but eventually sometimes becoming pale brown and minutely verruculose, with an apical cap-like mucous appendage.
Teleomorph: Stromata to 1500 x 600 µm, elliptical in surface view, very variable in development, ranging from individual ascomata formed within rust sori to the whole sorus being transformed into a stroma with 5-10 ascomata visible from the surface as black conical to hemispherical protruding ostioles; the stromatal wall black, composed of heavily melanized and occluded fungal cells. Ascomata 120-150 µm diam, globose, perithecial, usually immersed in stromatic tissues, the neck conspicuously papillate, conical to hemispherical. Subiculum absent. Peridium composed of several layers of fairly thick-walled laterally compressed textura angularis with cells to 12 µm diam, rather variably pigmented and sometimes hardly distinguishable from the internal stromatic tissue, the cells of the neck region smaller, thicker-walled and more strongly pigmented. Interascal tissue composed of fairly thick-walled remotely septate cellular pseudoparaphyses to ca 2 µm diam, without a mucous coating. Asci 58-74 x 9-11 µm, cylindric-clavate, tapering gradually from near the apex to a short stalk, fairly thick-walled, fissitunicate, the apex obtuse to rounded with an ocular chamber often visible, 8-spored. Ascospores arranged biseriately, 15-21 x 4-5.5 µm, fusiform-ellipsoidal, 1- or 2- (rarely 3-septate), constricted at the primary septum, the apical cell slightly wider and more conical, straight or slightly curved, usually hyaline but sometimes becoming pale yellowish brown (when ascospores are 2-septate), thin-walled, smooth, without a mucous sheath or appendages.