I'm going to take a chance here and assume, for the time being, that Epilobium latifolium (now Chamerion latifolium) is still a valid one to kick off this forum... ? (Since "Zauchneria" [lately renamed as Epilobium] is listed here as such, I think I'm on solid footing (?), but if not, moderators, please feel free to move or nuke this posting! :))
Arctic fireweed, or river beauty, occurs here over a wide elevation range from montane gravel bars (photo #1) to the high alpine (photos 2-5, where a hint of purple in the scree gradually resolves itself into bands of bloom, as one approaches) - wherever there is ample moisture, at surface, or running beneath the scree. It is a pleasure to see, whether up high or in less lofty areas.
I have just read that the species has a distribution that seems rather curious - though described as "essentially circumpolar and circumboreal", it is said to be absent from most of Europe, but present through the Himalayas and other Asian ranges:
It seems remarkable that the same subspecies occurs in the mountains of Pakistan as is said to occur here (ssp. latifolium)!
Looking through my photos, it seems petal width can vary considerably around here - from the very spiky flower (second last photo) to the round, full one (last photo).
What flower forms occur in your areas, or that you have seen in your travels?
There is some variation here too. The first image is from Greenland, the second two from Newfoundland.