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.