Can you identify this plant?

Mike Wiltshire, Kidderminster

Stefan says: A mystery plant has been growing in the cracks in your pavement and, each year, you have dug them out. This time you decided to pot up one of them and it has now thrown out what you call a long thread, which developed another plant. You’re keeping it in your greenhouse, although you don’t need to as it will be perfectly hardy.

It’s a form of our native bugle, Ajuga reptans, perhaps the variety called ‘Catlin’s Giant’, which has especially large leaves and it makes a fine ground cover in shady, damp places. Yours has produced a runner and this is how the plant spreads to cover the ground. It will produce spikes of lovely rich blue flowers in spring and early summer and I have it growing in my shade border along with astrantias, Geranium tuberosum and other shade-loving plants.