Rhododendron (Rhododendron ponticum) is another plant introduced to the UK during the 19th Century by the Victorian Horticulturalists.
It was planted in gardens but more crucially planted as cover for game birds on Sporting Estates and it is probably the later which accelerated this species break in to the wild.
It is a much greater problem in Western Regions, where the mild and moist climate suits it perfectly, and has infested native and commercial woodlands in a devastating fashion, as it is highly tolerant of shade and is able to grow in as little as 2% light.
It can be difficult to control forming dense impenetrable thickets that are difficult to treat, and is a threat to biodiversity, out-competing native species and monopolising local environments; Rhododendron exudes phenolic chemicals into the soil around them to suppress competing vegetation.
It is a particular problem invading ancient native woodlands which are fragile ecosystems which become unable to regenerate.