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