"Life in the garden takes many shapes and sizes but one of the strangest is galls. Galls are abnormal growths on a plant caused by a parasite.
I found these galls on a fallen oak leaf today. The doughnut shaped ones are Silk Button Galls (Neuroterus numismalis) and the green-coloured ones are Common Spangle Galls (Neuroterus quercusbaccarum). They are tiny. The diameter of the Silk Button is about 3 mm.