In my Flora Britannica, Richard Mabey relates

Monkeyflower, Mimulus guttatus, was first discovered and brought to English gardens from the damp and foggy islands off the Alaskan coast in 1812. But it crops up in damp places right down the west coast of America, as far south as the mountains of New Mexico, and it has been just as catholic in its choice of British habitats since it was first naturalised in the 1820s. It now occurs by the banks of burns, streams, lowland lakes, rivers and canals throughout Britain.

Given that last sentence, I can’t believe it’s taken me so many years to see Monkeyflower for myself but, during Wednesday’s walk around Cardiff’s Roath Park, I saw several of these plants, both around Roath Lake and along Roath Brook.