Pimple like swellings on the underside of a cowberry leaf (Vaccinium vitis-idae).
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
Doesn't quite fit the description I have for that - have you had a look to see if there is anything inside?
Opening up the swelling on the leaf shown above the rib in the left photograph revealed a doubling in thickness with a hard mass of fibres.
OK, so no invertebrate connection then. If you email me directly with the photos attached I'll try our fungus expert at Kew. (petershirley@blueyonder .co.uk)
Unfortunately, I am can't provide an identification for these leave spots from a photo. It might very well be fungus. There are serveral ascomycetes infecting cowberry leaves (a closer look, possibly microscopic examination would be needed to varify this). Exobasidium infections on cowberry leaves cause rather thick and conspicuous, brightly coloured galls.
Lat/Lng: 52.5, -3.0
OS grid ref: SO3698