Mahonia Rust - Cumminsiella mirabilissima

The rust fungus Cumminsiella mirabilissima affects the leaves of Berberis repens, Mahonia aquifolium and Mahonia japonica.  There is no host-plant alternation.  Aecia are orange and on leaf undersides; with a corresponding blackish spot above, usually on young leaves. Aecia may also form on fruits. Later, brown sori containing urediniospores and teliospores develop on leaf undersides.

Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features then in the comments box describe the size and identifying characters you have observed.

Widespread in much of Britain.

Status in Leicestershire and Rutland not known.