Himalayan Balsam

 Extract from this article.

An alien plant, so bothersome that Royal Marines have been called in to try to eradicate it, and so persistent that a top laboratory is working on a biological “secret weapon” to defeat it, has been helped to invade the British countryside by a fifth column of subversive flower lovers.

The Himalayan balsam grows up to 10ft (3m) tall and has colonised large areas beside rivers and woods throughout Britain, smothering any indigenous plants. The Environment Agency, Plantlife, Wildlife Trusts and the National Trust all say the species is a headache, and its total removal could cost as much as £300m.

But, with its pink orchid-like flowers, it is also attractive to many people. It’s so attractive, in fact, that a big factor in its invasive spread is people scattering its seed in the wild, according to research by Professor Ian Rotherham of Sheffield Hallam University and author of Invasive and Introduced Plants and Animals.

The upshot is that there is barely a part of lowland Britain free of this pretty menace. Fat stands of it clog small streams in places such as Somerset, and mass on the banks of rivers and woods from Cornwall to Scotland, with Norfolk, the Isle of Wight, New Forest, Hampshire, County Durham, Yorkshire, west Cumbria, Lancashire and North and South Wales especially troubled by it. The species is so prolific near Liverpool that it is known there as “Mersey weed”. Himalayan balsam grows in almost impenetrable thickets and will bully out any other species; its plentiful nectar means that bumble bees pollinate it rather than native species, and, being an annual, it dies down, leaving riverbanks bare in winter.

 It's interesting to consider that fact that this is an invasive species, yet has spread so far because people have found it to be so attractive! Using it's flowers as a means to spread further.