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It doesn't look hairy enough to be E. hirsutum to me.
The leaves are not the right shape for montanum (not broad enough). Most likely E. obscurum. Not clear enough to check the glands.
Epilobium montanum sometimes does have leaves as narrow as this - I usually spend time trying to make such plants hybrids (and possibly this could be ciliatum x montanum). However, the flower buds look more like pure montanum.
Perhaps such plants could be backcrosses, but as they have well-formed cross-shaped stigmas and are fully fertile, I accept them as being part of the variation of E. montanum.
I don't think the leaf-shape and veining in the photo matches E. obscurum.
I think Will Avery may be right, but it looks best that the current favoured ID is just to genus.
That's what obscurum looks like round here and montanum is quite different, but there is always more to learn! Hybrids muddy the waters! Best to wait til they are fully developed.
I think this discussion illustrates the difficulty of these plants. Both Cicuta and I have long experience, and his comment, "That's what obscurum looks like round here," may be highly relevant. These plants are essentially weedy, self-fertilising and rapidly build up large populations. Under such circumstances we can expect locally pure-breeding lines to exist and what may be fairly uniform morphology in one area might not be quite matched elsewhere.
A really good account of these plants is included in Flora Nordica vol. 6, published in 2010. [An excellent series, lots of line illustrations, vols. 3-5 not published yet.]
However, after being tied up with exam marking/processing for the last three weeks I have been relaxing by wandering round, checking local populations and refreshing my knowledge of detail of these plants. I maintain my opinions as expressed above. I still think identification of the above photographs just to genus is safest, but I also still maintain that they could very easily be E. montanum.
1) The flower buds are relatively large and soon start to droop. This matches E. montanum (and also E. roseum but it isn't that) and does not match E. obscurum, in which the plant, as I know it here, has buds that remain rather stiffly erect. Putative hybrids, E. montanum x obscurum (rather young but with malformed stigmas as one expects with this cross and clearly intermediate vegetatively), also have buds that remain more or less erect.
E. ciliatum has buds that are somewhat more divergent, but not, in my experience to the extent shown here. Plants of E. ciliatum x obscurum (a common hybrid) that I looked at today had buds that were erect as in the obscurum parent, and E. ciliatum x montanum that I looked at today had buds that were much like E. ciliatum but a little larger. Nevertheless, this hybrid is very variable and I wouldn't rule it out as an identity for the photograph above, and this would explain the narrow leaves.
2) The leaf toothing of E. montanum is distinct from the other species in that the teeth are very numerous, small and quite delicately pointed. The feature can be carried over into its hybrids.
E. obscurum, by contrast, at least in my area, has quite distant and very obscure teeth. I looked at quite a lot of plants and found no exceptions, including those with rather broader leaves than usual. The plants in the photographs above have montanum-type toothing.
So personally I still think this is most likely a narrow-leaved montanum. But as Cicuta says, "Best to wait til they are fully developed." Yes indeed.
Quite good wandering around. I found one convincing plant of obscurum x parviflorum, which I think I have seen only once before, and E. roseum looks like it will have a good year, though not in flower yet. Also two good lichens - but on stonework that is soon to be cleaned. :-(
I must confess I saw a flowering montanum which otherwise looked just like this last weekend in Denbighs.
Lat/Lng: 54.710784, -1.694306
OS grid ref: NZ197351