Growing luxuriently on verges around the neigbourhood. I had previously thought this to be some kind of clover, but looking more closely can see the burrs forming already.
Burr medic, also known as burr weed, is a type of trifoliate weed that can quickly spread throughout the lawn and garden if not controlled. You can recognize this weed by its green serrated leaves and reddish-purple colored stems that creep closely along the ground. It also has small yellow flowers. After flowering, the tiny green pods produce prickly burrs. These will eventually dry up and turn brown, spreading seeds everywhere. (Gardening Know How website)