Myriogenospora atramentosa (Berk & Curt.) Diehl has been found on species of Paspalum, Andropogon, Eragrostis, and Panicum in surveys of pastures with histories of toxicity problems in cattle. The fungus produces a systemic infection in which growth on the host is entirely superficial. Infection of each leaf and inflorescence occurs from mycelium in the bud. In the upper part of the leaf one side of the blade remains unexpanded and is bound into a tight roll by a mass of fungus plectenchyma that it encloses. Branches of the inflorescence are enmeshed in a fungus matrix and remain enclosed within the flag leaf sheath. Superficial, linear, black stromata form down the middle of the leaf alongside the leaf roll and in the juncture between margins of the flag leaf sheath. The stromata produce fusoid conidia in a fleeting early stage. Immersed perithecia develop in a longitudinal row in the stroma. The cluster of aparaphysate asci on a basal cushion, lateral paraphyses, and indistinct peridia of the perithecia are characteristic of the Clavicipitaceae. The numerous fusoid spores in the swollen asci are part-spores derived from fragmentation of eight filiform, septate ascospores. The refractive cap at the apex of the ascus is a modification of the typical clavicipitaceous structure. Myriogenospora is placed in the tribe Balansiae of the Clavicipitaceae.