I looked around a large disused sand quarry today and was amazed at how Ragwort (Senecio jacobaea) had so completely taken over a large area of many acres, it had formed an actual 'forest' with many large plants averaging 4-5ft but the tallest just over 6ft! (ragwort is usually about 3ft-4ft high).
I've never seen any plant so totally dominate such a large area, it was a sea of yellow with only the odd spear thistle or stinging nettle being present.
Ragwort isn't strictly 'invasive' in Britain as its a native plant but this shows its incredible potential to run out of control. I suspect the reason it did so well here was that being an old quarry its fairly sheltered from winds and the seeds mostly end up landing close by, resulting in the very dense growth seen. If it was in a more exposed place the seeds would likely be scattered far and wide by the wind.
