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.

The one growing along railway lines is usually pretty rampant. But I
have seen in particularly in gardens up north with heavy clay soils
barely able to put up more than two or three shoots each season and
entirely self limiting in growth. Same for the low growing bindweed
(though not the more brutal common C. arvensis)

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.

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,

Curiouser and curiouser.

Whatever form it is I recall that it sets copious amounts of fluffy
seeds and ISTR they were viable. It also spreads by thin underground
runners/rhizomes and is very vigorous - able to hold its own and even
win against nettles and brambles on an embankment.

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

Is there an easy way to tell the cytotypes apart without an oil
immersion microscope and fancy DNA stains?

I probably still have access to a sample of the weak and feeble form.

In this neck of the woods Convolvulus arvensis is relatively rare. It's

I quite like it. Doesn't grow much like a weed on heavy clay for me.

less than a tenth as common as Calystegia silvatica and Calystegia
sepium, and is also rarer than Calystegia pulchra. Even black bindweed
(Fallopia convolvulus) - a weed of maize fields - is commoner

I think local conditions play a big part although common hedge bindweed
is a potent smothering weed even in robust country hedgerows. I suspect
the ornamental ones could be a nuisance if they were winter hardy.

--
Regards,
Martin Brown