On 16/09/2019 21:18, Chris Hogg wrote:
On Mon, 16 Sep 2019 18:33:35 +0100, Martin Brown
wrote:

On 16/09/2019 17:59, David Rance wrote:
On Mon, 16 Sep 2019 12:10:50 Nick Maclaren wrote:

In article ,
Martin BrownÂ* wrote:

Himalayan balsam is becoming quite a problem in North Yorkshire on
stream and river banks wiping out almost everything else and spreading
rapidly. Only Japanese knotweed out competes it. Nettles and rosebay
willow herb both die out after a few years leaving a monoculture.

I have never seen it do that, and I have been looking out for it for
several decades now.Â* I believe you that it is a (very) localised
problem, but it assuredly isn't a widespread one.Â* Every apparent

I can well believe that it is only a local difficulty, but it seems to
be incredibly effective at moving along water courses and colonising the
banks to the near exclusion of everything else unless treated promptly.
Its flowers smell quite nice in the evenings a bit like bizzy lizzies on
steroids the explosive seed capsules pack more of a punch.

monoculture of it I have looked at has turned out to be, on closer
inspection, merely that it dominates the top layer and there is a
wide range of other species underneath it.

Only if you count grasses which do seem to hang on in the margins.

Interesting about rosebay willowherb (or should it be rose bay willow
herb? - I've never been sure). I remember my father pointing out to me
the way that it colonised bomb sites during the second world war
especially in London. Then for most of my life it seemed to have
disappeared only to reappear in the last few years, and for the first
time I have some springing up in my garden.

I remember the rosebay willow herb of my youth being a much more
vigorous invasive weed in Manchester on a sandy soil. On my North
Yorkshire heavy clay it barely survives and is seldom seen in hedgerows
here except on or near railway enbankments.

Are there multiple sorts or is it very sensitive to local conditions?

Aka 'fireweed', from it's habit of appearing on areas recently burnt.

Bees like it, and I've always understood from the time I kept them
that there's a 'lesser' and a 'greater' willow herb, but looking in my
wild-flower book I see there are several in the willow herb family,
and hybrids are common. SRH will be along soon to give the definitive
reply.


Rosebay willowherb is the only British species of the genus
Chamaenerion. Chamaenerion is the sister group to the genus Epilobium,
which contains the rest of the British willow herbs. The great
willowherb, Epilobium hirsutum, is about the same size of rosebay, and
tends to damp habitats, such as ditches and canal banks. There are
several smaller, mostly ruderal (Epilobium montanum also occurs in
woodland), species, which are difficult to tell apart - I can manage two
of them - and some species of wet upland habitats including the New
Zealand willowherb, Epilobium brunnescens. And hybrids are indeed said
to be common - I've only seen the one definite hybrid, but my failure to
identify the other species might well be due to be confused by hybrids.

On Monday, 16 September 2019 21:58:05 UTC+1, Nick Maclaren wrote:
In article ,
Stewart Robert Hinsley wrote:
On 16/09/2019 18:33, Martin Brown wrote:

I remember the rosebay willow herb of my youth being a much more
vigorous invasive weed in Manchester on a sandy soil. On my North
Yorkshire heavy clay it barely survives and is seldom seen in hedgerows
here except on or near railway enbankments.

Yes. It's definitely a plant of well-drained soils.

Are there multiple sorts or is it very sensitive to local conditions?

The genus has 8 recognised species, but only one is in the British
Flora. (A second species occurs as a rare garden escape.) However in
North America at least there are two cytotypes (cryptic species) of
Chamaenerion angustifolium, with mostly disjunct distributions.
Supposedly it was a relatively rare plant prior to WWII, and became
somewhat invasive afterwards. I wonder whether a non-native strain was
introduced.

As I was born in a far country in 1947, I cannot say :-) But my
definite recollection is that it because far more widespread in the
1960s and 1970s. That is a very plausible hypothesis.


Regards,
Nick Maclaren.

It's all over our heavy clay garden.

Jonathan

On 16/09/2019 19:09, Stewart Robert Hinsley wrote:
On 16/09/2019 18:33, Martin Brown wrote:

I remember the rosebay willow herb of my youth being a much more
vigorous invasive weed in Manchester on a sandy soil. On my North
Yorkshire heavy clay it barely survives and is seldom seen in
hedgerows here except on or near railway enbankments.

Are there multiple sorts or is it very sensitive to local conditions?


The genus has 8 recognised species, but only one is in the British
Flora. (A second species occurs as a rare garden escape.) However in
North America at least there are two cytotypes (cryptic species) of
Chamaenerion angustifolium, with mostly disjunct distributions.
Supposedly it was a relatively rare plant prior to WWII, and became
somewhat invasive afterwards. I wonder whether a non-native strain was
introduced.

It may be just coincidence but where I know the vigorous strain from was
about 2 miles from a major US encampment of soldiers in Manchester
during WWII. Bomb damage and railway bankings were its main habitat.

The non-vigorous version is up in Newcastle and it barely clings on to
life on clay in a slightly overgrown herbaceous border. I prevent it
setting seed but it is nothing like the potent weed that I remember.

It's my 24th most recorded plant, coming in behind Dryopteris filix-mas
and Senecio vulgaris, and ahead of Epilobium hirsutum.

Increasingly ragwort aka Jacobaea vulgaris is becoming very common in
the countryside round here. There is a ragwort control act 2003 but it
isn't worth the paper (or is it still vellum) that it is printed on.

--
Regards,
Martin Brown

On 19/09/2019 18:50, Martin Brown wrote:
On 16/09/2019 19:09, Stewart Robert Hinsley wrote:
On 16/09/2019 18:33, Martin Brown wrote:

I remember the rosebay willow herb of my youth being a much more
vigorous invasive weed in Manchester on a sandy soil. On my North
Yorkshire heavy clay it barely survives and is seldom seen in
hedgerows here except on or near railway enbankments.

Are there multiple sorts or is it very sensitive to local conditions?


The genus has 8 recognised species, but only one is in the British
Flora. (A second species occurs as a rare garden escape.) However in
North America at least there are two cytotypes (cryptic species) of
Chamaenerion angustifolium, with mostly disjunct distributions.
Supposedly it was a relatively rare plant prior to WWII, and became
somewhat invasive afterwards. I wonder whether a non-native strain was
introduced.

It may be just coincidence but where I know the vigorous strain from was
about 2 miles from a major US encampment of soldiers in Manchester
during WWII. Bomb damage and railway bankings were its main habitat.

The non-vigorous version is up in Newcastle and it barely clings on to
life on clay in a slightly overgrown herbaceous border. I prevent it
setting seed but it is nothing like the potent weed that I remember.

It's my 24th most recorded plant, coming in behind Dryopteris
filix-mas and Senecio vulgaris, and ahead of Epilobium hirsutum.

Increasingly ragwort aka Jacobaea vulgaris is becoming very common in
the countryside round here. There is a ragwort control act 2003 but it
isn't worth the paper (or is it still vellum) that it is printed on.


Ragwort is my 15th equal (with great plantain) recorded plant.

--
SRH