Pucciniastrum epilobii  

Spermogonia hypophyllous, abundant, ca 100 µm diam. and 25 µm high, hemispherical with the central part flattened, subcuticular. Spermogonia 1.5-3 µm in length, ovoid.
Aecia hypophyllous, usually in two rows, cylindrical, ca 250 µm diam. and 1 mm high, whitish, splitting above or rarely at the sides, soon breaking down. Peridium composed of vertically elongate polyhedral cells 25-42 x 10-16 µm in size, the outer wall smooth and the inner wall minutely verrucose. Aeciospores 14-21 x 10-14 µm, subglobose, ellipsoidal or ovoid, the wall 1-1.5 µm thick, the wall minutely verrucose with a smooth spot on one side.
Uredinia mostly hypophyllous or on stems, scattered or in groups, 100-250 µm diam., ± hemispherical, eventually opening with an apical pore, yellowish, the upper wall breaking down to reveal the pulverulent contents. Peridium rather thin, composed of angular thick-walled cells 10-18 µm in diam. Urediniospores 15-23 x 10-15 µm, ovoid or ellipsoidal, the wall 1-1.5 µm thick, hyaline, remotely and shortly echinulate.
Telia hypophyllous, rarely epiphyllous or on stems, 100-200 µm diam., mostly in groups, subepidermal, pale brown. Teliospores intercellular, 2- or 4-celled, the 2-celled spores 18-28 x 7-15 µm and the 4-celled spores 20-30 µm diam., the lateral wall 1-1.5 µm thick, to ca 3 µm at the apex, brown, smooth, with a single pore towards the apex.