Uredinia on both surfaces of leaf, scattered or grouped, confluent, elongate, to 8 mm long, surrounded by the ruptured epidermis, dark cinnamon-brown. Urediniospores (27-) 35-42 x (20-) 26-32 µm, broadly ellipsoidal to obovoid, cinnamon-brown, wall 2-2·5 µm thick, very finely and often remotely echinulate with spines scattered over the surface, with 3 (rarely 4) ± equatorial pores, the pedicel hyaline and usually dehiscent.
Telia similar in external form to the uredinia, blackish-brown. Teliospores 42-51 x 18-26 µm, ellipsoidal to clavate, the apex rounded to obtuse, usually narrowed below, somewhat constricted at the ± median septum, dark chestnut-brown, paler below, wall 1-2 µm thick at the sides, greatly thickened (to ca 9µm) in the apical part, smooth, the pedicel brownish, to one-third the length of the spore, persistent.
Not formally evaluated. Recently recorded from E Norfolk after a gap of over 50 years, but the species is very probably under-recorded and more surveys are needed. The host plant is designated as of Least Concern, but the fungus appears to have a rather less extensive distribution in GB&I than does its host.
Apparently restricted to living leaves of Cladium mariscus. Uredinia are sometimes parasitized by the common rust-inhabiting Eudarluca caricis.
In GB&I, recorded only from VC29 Cambridgeshire and VC27 E Norfolk, as uredinia. Telia of this species have apparently never been recorded in our region.
A biotrophic parasite that has not been recorded as causing significant damage to its host plant.