I see this plant so very often that I would’ve sworn it was a native British wildflower but no! Ivy-leaved toadflax (Cymbalaria muralis) only came to Britain in the early 1600s. In his excellent book Weeds: How vagabond plants gatecrashed and changed the way we think about nature (Profile Books, London, 2010), author Richard Mabey relates the story that the plant’s seeds ‘were caught up in the packing of some marble statuary imported from Italy to Oxford, whence, like the city’s eponymous ragwort, they migrated into the wider world via the college walls’. This explains why Ivy-leaved toadflax was, for a time, known as ‘Oxford weed’, though it has accumulated several other common names as well: Kenilworth ivy, coliseum ivy, mother of thousands, and pennywort.
Ivy-leaved toadflax came originally from the mountains of southern Europe but, in Britain and many other parts of the world, it has swapped alpine rocks and stones for the bricks and stones of man-made walls. Its pretty little snapdragon-like flowers can be seen from April through to September.