Officially, Winter heliotrope (Petasites fragrans) is a non-native invasive; unofficially, I think it’s got a rather lovely flower, which is particularly nice to see in the dead of winter, and its vanilla smell is divine.
According to Mabey’s Flora Britannica, it was brought to Britain as a garden plant in 1806, and the GB non-native species secretariat website states that it was first recorded in 1835 – presumably they mean the first record of it straying outside the bounds of the gardens where it had been planted. Though native to the Mediterranean and North Africa, it’s made itself at home in Britain, where it favours roadside verges, woodland margins and rough grassland. It seems very adaptable: in my local area, it favours sloping banks, a sunny slope in Dingle Park and a very wet and shady, steeply sloping streamside in Alexandra Park.
It can be difficult to get rid of because it grows very readily from the smallest discarded stem, sending its ‘roots’ (actually underground stems called rhizomes) spreading horizontally in all directions. Sneaky!