Pat Bennett/Alamy
IN THE past, horticulturalists brought thousands of new plant species from distant lands to the UK, and some have became staples in gardens. A few have spread beyond the fence to grow in the wild and are so vigorous they have taken over local ecosystems.
Well-known examples include Japanese knotweed, which can poke up through asphalt, and rhododendrons, which colonise woodlands, densely covering the forest floor. Purple pampas grass, from South America, loved in many suburban gardens for its huge, showy plumes, is a menace on rocky coasts where it crowds out native species.
Even floating pennywort (pictured), an attractive…
