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.

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