The largest of the circles is about 4 mm in diameter.
Each circle consists of several small blisters full of tiny brown granules or spores. On some leaves, the blisters are arranged more randomly and not in circles. The blisters open, and after a while, little orange-white larvae appear, but they soon drop off and, in a few days, die. I thought I had some pictures of the larvae, but I can't find them at the moment. [Edit: larva