First one is Joe Pye Weed or Eutrochium, as you thought.
Not sure about the second one, familiar though.

If the second one isn't Japanese Knotweed it looks like a very close relative and should be treated with caution.

Thank you Owd. Thanks Bulbaholic. I've added a further picture of the second one, to give some scale.

Well its most definitely not Japanese Knotweed. I suspect its one of the Viburnums, just not sure what though. I strongly suspect V. plicatum, but the flowers aren't quite right... although others on the bush may be.

Thanks Bamboo. It does resemble Viburnum now you say.

Pye weed seems to apply to both Eupatorium and Eutrochium. They look so similar, are they the same thing?
I thought this one was Eupatorium.

I still call this plant Eupatorium purpureum, Steragram, but the classification has been changed - the genus has been split and some plants have been reassigned to other genera, so now some are Eutrochium, some Conoclinium, some Ageratina. But some are still Eupatorium, and this particular one is shown on the web as both Eupatorium purpureum and Eutrochium purpureum. Clear as mud, ain't it...

Great - that sorts that one then (though I haven't a hope of remembering it...) What is E. cannabinum now - at least I can make a note of that in my wild flower books?

Well according to the internet, its still a Eupatorium...

I still refer to crocosmia as montbretia at times.

Many people do Dawnsaunt, but its a bit different - montbretia was always just a common name, not a botanical one, whereas Eupatorium is a botanical name...It's all that plant DNA research that's causing reclassification of botanical names.

Thankyou Bamboo.

I see. Thanks for that, interesting.