Puccinia glechomatis
The rust fungus Puccinia glechomatis galls the leaves of Ground-ivy affecting the stem, petiole or underside of the leaf veins. The areas become swollen, yellow, brown or black bearing telia, each up to 1 mm across, usually in groups up to 4 mm across.

The only rust on Glechoma hederacea is P. glechomatis and it is only ever found in the telial state which appears as a circle of tiny brownish dots usually on the underside of the leaf.
Where the host plants occur.
When the host species are in leaf, but especially around September.
Widespread and fairly frequent in Britain.
Status in Leicestershire and Rutland not known.
Leicestershire & Rutland Map
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MAP KEY:
Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015