Ustanciosporium gigantosporum  

Sori surrounding rudiments of host tissue at the tip of the axis of sterile spikelets, with stunted glumes. Sori spherical to ovoid, approximately 1 x 1-1.5 mm in size; when young, hidden in the glumes and exposed when old, without a peridium or sterile stroma, with spores developing in a hyaline matrix on the surface of the host tissue. Spore mass agglutinated at the base, powdery in the upper part, dark. Ustilospores (teliospores) 11-14(-15) x (15-)17-19(-20) x (16-)18-21(-24) µm, single (not aggregated into clumps), subglobose to flattened, in plane view circular to ± bluntly angular; light to medium reddish to olive brown, sometimes with hyaline appendages. Walls approximately 1 µm thick, thinner on both flattened sides, finely and densely foveolate-reticulate.

Description derived from Piepenbring (2000).

Map of known distribution in Great Britain and Ireland.