In article ,
Martin Brown wrote:
On 21/05/2012 13:13, Stewart Robert Hinsley wrote:
In message , Martin Brown
writes

Rosebay Willow Herb is another of these curious weeds that is
sometimes absolutely rampant and a serious menace or elsewhere barely
able to eke out a living. I have never been able to figure out whether
there are different cultivars of it or some soils do not suit it.
Seems to be more likely to go rampant in well drained fertile soils.

Actually, most weeds are like that. The reason that the UK has so
many that are ubiquitous is that the populated parts of the UK have
a very narrow range of climate and pretty similar soil types. But,
even here, there are only a minority that are a problem everywhere.

Supposedly in the 19th century rosebay willowherb was an innocuous
plant, and it didn't become invasive until the 20th century.

I have heard tell that the railways are to blame for spreading it and
also WWII bombsites. I don't know if there is any truth in either.

The former, almost certainly, much as with buddleia, by providing
suitable corridors. But it grew in the latter merely because it
is a fairly dominant weed of exposed, poor soils (such as rubble!)
It might have spread it around London, but most of the country had
very sparse bombsites.

I doubt that any more is known about why plants suddenly become
invasive than why animals do. For those, I mention merely the
norwegian rat, the rabbit and the collared dove - of those, I have
heard plausible but unproven explanations of the last, and know
of none of the first two (though I haven't looked hard).

There are three cytotypes - Chamaerion angustifolium (diploid),
Chamaerion platyphyllum (tetraploid) and Chamaerion danielsii
(hexaploid). I wonder whether it's just one of them which is invasive,

and that this one wasn't present in Britain (much) before the 20th
century. [British botanists don't make a distinction between the
cytotypes.]

That wouldn't be a first time!


Regards,
Nick Maclaren.