Puccinia oxalidis  

Spermogonia: unknown.
Aecia: unknown in GBI material.
Uredinia: hypophyllous, in roundish to irregular clusters 1-3 mm across, often confluent, powdery, bright yellow, sometimes mixed with telia. Urediniospores (17-) 19-21 (-23) x (14-) 16-18.5 (-19.5) µm, ovoid to ellipsoidal or subglobose, the wall thin (ca 1.5 µm thick, measurements in water), finely echinulate, the spines ca I µm in height; pores several, inconspicuous; the pedicel thick-walled, ± cylindrical, rarely remaining attached.
Telia: very small, hypophyllous, waxy in appearance. Teliospores 22-29 x 13-15 µm (measured in warmed lactic acid), the length/breadth ratio rather variable, ± clavate, 2-celled, not or hardly constricted at the septum, hyaline to pale yellow, smooth, thin-walled.