Phragmidium

Phragmidium is a genus of rust fungus that typically infects plant species in the family Rosaceae. It is characterised by having stalked teliospores borne on telia each having a row of four or more cells. All species have a caeoma which is a diffuse aecidium lacking a peridium. There are a number of species of Phragmidium, most of which are restricted to one or a few host species. Examples include: Phragmidium acuminatum on Rubus saxatile Phragmidium bulbosum on Rubus fruticosus and Rubeus caesius Phragmidium mucronatum Phragmidium sterilis on Potentilla sterilis Phragmidium potentillae on Potentilla anglica Phragmidium rosae-pimpinellifoliae Phragmidium rubi-idaei on raspberry Phragmidium tuberculatum on some rose cultivars Phragmidium violaceum on cultivated blackberry and loganberry Possibly the most commonly encountered is P. mucronatum, found on most species of wild roses including Rosa canina and Rosa arvensis....read more on Wikipedia.