Up to six feet tall.
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Note that the size of this plant is 6feet! It cannot be common Valerian.
University of Edinburgh and Biodiversity Observatory (OU)
Plenty of Common Valerian growing through brambles in a local wood gets to over 6 ft tall, as does some growing in drainage ditches beside a local canal. I know, because some of it is too tall for me to photograph hoverflies on top of the flowers...way over my head! I'm not saying its definitely that shown, but it can grow that tall. Also bear in mind that estimations of size are often well out, in fact.
My Flickr photos...
I see, well so far common valerian is winning, for what that is worth.
It would help to know whether it was growing in the wild or in a garden, say. Closing in on the location given suggests it is countryside, but that may not be an accurate idea of where it was seen.
I grow lots of this in my garden and the image to my mind definitely has the "feel" of Verbena bonariensis. As I said in my original comment, we cannot see much of the foliage.
David J Trevan
I grow it too and I agree!
I note that this species is listed in Stace as an occasional garden escape.
In the horticultural world it is known as a "see through plant", as it makes an excellent display but you can still see through a mass planting of it!
Also while I can appreciate some stems growing through brambles, in this image they are all very tall so I'm not convinced that this is Common Valerian!
And it has been seen as an escape on iSpot before.
because it has (three) stamens sticking out.
Verbena has four stamens included in the tube and not visible.
... the sizes given in books, and generally encountered, aren't absolute limits. Stace says that Malva sylvestris reaches 1m, exceptionally 1.5m, but I've seen a plant at over 2.5m.
Blimey! Must have been on a compost heap or something.
... in a hedgerow by a canal towpath. I collected seed, but the offspring weren't so big.
Lat/Lng: 50.6, -2.1
OS grid ref: SY9581