In message , kay
writes

Rachel 101;919717 Wrote:
Thank you so much for all the replies - it's really good of you all.

Kay, the leaves are not hairy, and neither is the stem: sorry again, I
should have made that clear.


No, it was my english that was the problem - I was rejecting those
suggestions on the grounds that they were hairy, which yours most
clearly wasn't.

Yours looks exactly like "the other" weedy species of Epilobium, and I'm
never sure which that is, having never sat down with a key and
identified it. But I noticed one yesterday in my garden, and thought
"that looks exactly like the one on urg". Problem is, it only grows to
about 1 foot or 18inches high. The red colouring can be a function of
cultivation - eg drier soil. The one I was looking at was growing out of
an old brick wall and definitely had he red colouring.

So - forgive me for suggesting this - is it possible a) that you're
wrong about the 3-4ft b) that the plant you've photographed is growing
close to the 3-4ft one but isn't it? I have the weedy Epilobium growing
in and amongst rosebay, and when I'm weeding in early spring it's easy
to get them muddled, even though they are so different.

Incidentally Fitter et al describe E montanum as "short to medium" which
is up to 2ft.

Poland ("Vegetative key to the British Flora" gives "to 75cm" for both
E. parviflorum and E. montanum. He also says that E. montanum often has
red stems. (It was my impression that E. parviflorum was the most likely
to show red stems.)

Of the hairy-leaved species he says that E. hirsutum has stem-clasping
to decurrent leaves, and E. parvifolium sessile to shortly petiolate
leaves. Reading between the lines, the extreme forms can be
distinguished to species by the nature of the leaf attachments, but the
intermediate forms can't.

Willowherbs have a tendency to have alternate leaves higher up the stem.
Poland says that this tendency is stronger in E. hirsutum than E.
parviflorum.

I think you're going to have to let one plant of it flower - it's the
only way you're going to get an id.

Poland does give a vegetative key to Epilobium. But it depends on the
use of a hand lens - one batch of three species is keyed out by the
presence of fine hairs not visible to the naked eye (and from my
experience not detectable by touch either, which works with some other
taxa).
--
Stewart Robert Hinsley