Spermogonia amphigenous or on the petioles, in little clusters of 6-10, brownish when old.
Aecia hypophyllous or on the petioles, usually surrounding the spermogonia in scattered roundish clusters (elongated on the petioles, to 15 mm long), at first hemispherical, then shortly cupulate, yellow, with short, torn, scarcely reflexed peridia; aeciospores 16-24 x 20-28 µm, globose or ellipsoidal, the wall finely verruculose, about 1 µm thick.
Uredinia generally hypophyllous, on small, pale yellow or brown spots, minute, scattered, surrounded by the erect epidermis, chestnut. Urediniospores 22-30 x 20-25 µm, ellipsoidal, cinnamon-brown, echinulate, the wall 1·5-2 µm thick, with 2 or 3 approximately equatorial pores.
Telia generally hypophyllous, irregularly scattered, minute, chocolate-brown; teliospores 35-60 x 24-35 µm, ellipsoidal to cylindrical, rounded or obtuse at both ends or narrowed below, slightly or not constricted at the septum, the wall delicately verruculose, uniformly 2-2·5 µm thick with a broad flat hyaline papilla over the apical pore, pore of lower cell ± depressed, pedicels nearly hyaline, short, deciduous.
Similar to Puccinia calthae but with broader, darker brown slghtly warted teliospores.
On living leaves of Caltha palustris.
Common throughout Great Britain, also recorded from western Ireland.