Spermogonia epiphyllous, in crowded groups in the paler centre of dark violet or reddish leaf spots, hemispherical. Spermatia ovoid.
Aecia hypophyllous or on the stems, caeomoid, often in rings around the spermogonia, to 5 mm diam. (larger and more elongate on the petioles and nerves), orange-yellow, surrounded by straight or slightly curved clavate paraphyses to 60 µm in length and 18 µm diam. Aeciospores 19-30 x 17-24 µm, broadly cylindrical to ellipsoidal, yellow, the wall 3-3.5 µm thick, distantly and strongly aculeate-verrucose, spines 4-5 µm apart.
Uredinia mostly hypophyllous, scattered, very small (less than 250 µm diam.), orange-yellow, surrounded by curved clavate paraphyses 45-60 µm long and 18-25 µm broad. Urediniospores 19-30 x 18-25 µm, globose to ellipsoidal, yellow, the wall 3-4.5 µm thick, distantly and strongly aculeate-verrucose, with indistinct pores.
Telia hypophyllous, 250-1000 µm diam., scattered, pulvinate, black, lacking paraphyses. Teliospores 65-100 x 30-36 µm, cylindrical, usually 4-celled but some with 2-5 cells, slightly constricted at the septa, the apex rounded with a hyaline papilla 3-4 µm in length, the base rounded, dark brown, the wall with scattered minute warts, with 2-4 pores in each cell, the pedicels to 190 µm long and 18 µm diam., hyaline, very thick-walled, swollen at the base.
Listed as of Least Concern for Wales by Woods et al. (2015) and would undoubtedly be assessed as of LC for the UK a a whole. It is a very common and widespread species.
Distinguished from other species of Phragmidium on Rubus by its usually 4-celled teliospores and aculeate-verrucose urediniospores.
On living leaves of Rubus fruticosus agg.
Throughout the British Isles.