This week, a species formerly or still (pending your acceptance of systematics nerdery) ascribed to Epilobium (oldy or misleady) or more accurately (accurently!) Chamerion: Chamerion angustifolium. Or so to speak, Fireweed (USA and most Canada), Great Willow-herb (parts of Canada), or Rosebay Willowherb (UK), and as litterally translated from French Epilobium with narrow leaves. Should have been appearing in an old BloggerBioBlitz (2008 edition).
Chamerion angustifolium
Just to quote wikipedia with regard to the systematic attribution:
This species has been placed in the genus Chamerion (sometimes, incorrectly, given as Chamaenerion) rather than Epilobium based on several morphological distinctions: spiral (rather than opposite or whorled) leaf arrangement; absence (rather than presence) of a hypanthium; subequal stamens (rather than stamens in two unequal whorls); zygomorphic (rather than actinomorphic) stamens and stigma. Under this taxonomic arrangement, Chamerion and Epilobium are monophyletic sister genera.
Take notice of the very distorted stigma compared to heavily bent stamens, suggesting pollination by big bees with the apparent aim for allocross (or xenogamy). (Wow, POTW should go for word of the week category rise it seems!).
Seeds Aside 
I often wondered why fireweed was included with Epilobium after seeing the other Epilobium species like E. strictum, E. leptophyllum, and E. coloratum. The whorled leaves of E. angustifolium and flowers without a floral tube (the other species have one) seemed like differences enough to place it next to rather than within Epilobium or at least in a subgenus.
Would it be more accurate to say of Chamerion’s stigma that it is exserted rather than distorted as it protrudes about 1/4 more the length of the anthers?
Another question: is Chamerion a monotypic genus?
Yep, that was definitely something weird, given the phenotypic departure, especially in the absence of some other uniting feature. Sometimes there’s a defining apomorphy in a Genus and you’d go with grouping otherwise quite different species.
I wonder about pollen dispersal in Chamerion angustifolium, because if I remember well all species in Epilobium disperse pollen as tetrads.
I don’t remember if the pollen is in tetrads or not. Will need to look that up and in a few months put some of the pollen under the microscope to see for myself.
I think there is a different leaf venation pattern in Chamerion angustifolium, too, but without a specimen at hand I can’t say for sure.