This introduction from America is a glabrous, annual weed of gardens and parks - which is exactly where we found it. The flowers are usually blue according to Stace and between 2 mm and 3 mm in diameter. These were white and less than 2mm and very hard to see but the leaves are quite distinctive.

The distribution is peculiar in that there is some round the London area, some in Cornwall, a little on the north coast of Scotland and it is common in Northern Ireland.