Pucciniastrum circaeae  

Uredinia mostly hypophyllous, subepidermal, scattered or gregarious, often covering the whole surface of the leaf, 1-1.5 mm diam., round, sometimes confluent, orange-yellow to pale yellow; peridia hemispherical, thin, dehiscent from a central pore, peridial cells small, irregularly polygonal, 8-18 µm diam., walls 1. 5-2 µm thick, colourless, smooth, the ostiolar cells larger, walls 1.8-3 µm thick, smooth. Urediniospores  16-24 x 12-16 µm, subglobose, ovoid or ellipsoidal, the wall 1-1.5 µm thick, minutely echinulate, contents orange-yellow when fresh.
Telia hypophyllous, subepidermal, very small, scarcely visible to the naked eye. Teliospores in little groups, 17-24 x 21-28 µm, roundish or flattened at the sides, divided longitudinally into 2-4 cells, the wall of uniform thickness (about 2µm), yellow, smooth.

Description adapted from Wilson & Henderson (1966).