It is my opinion that the name Epilobium oreganum Greene has been misapplied to plants of E. glandulosum ssp. glandulosum in the Sierra Nevada; plants with true 4-branched styles (topmost photo) have not been collected from the region. Presently, California Dept. of Fish and Game 'Rarefind' records have been corrected to reflect the absence of Epilobium oreganum in the Sierra, but the California Native Plant Society Inventory has not.
The problem arises because the key in Munz and Keck 1959 would direct long styled plants of E. glandulosum var. glandulosum to the name E. exaltatum E. Drew, which had a stated range in their Manual from the Sierra north to Oregon and Montana etc. Epilobium exaltatum E. Drew is a straight synonym of E. oreganum Greene, so the Munz & Keck application of that name was incorrect.
Several specimens were cited in older versions of NDDB as E. oreganum Greene from the Sierra:
JEPS72727 (EO#30) has not been annotated. I have inspected the specimen, but did not annotate it. My opinion is that the specimen is E. glandulosum var. glandulosum.
JEPS89974 (EO#36, Tulare County) is E. oregonense not E. oreganum.
UC1187138 (EO#39) is a specimen of E. oregonense
EO#40 & 41, 42, & 43 are records based on Gordon True's Nevada County Plant List, which in the list (my edition is 1973 mimeographed version) are records for E. exaltatum Drew, so again are E. glandulosum var. glandulosum
NDDB EO#29 is a report by Ledyard Stebbins from Wrights Lake. In his Wright's Lake Flora, Ledyard applied the name, probably Epilobium exaltatum via Munz's key, to this collection. Ledyard and Jack Major shared a cabin at Wrights Lake, and as their student, I was there many times. The plants grow in the meadow north of the cabin, and I have revisited and recollected the material, which is clearly E. glandulosum var. glandulosum (see the lowermost photo above). I suspect Ledyard's uncertainty is owing to the fact that c&nSNH plants of E. glandulosum var. glandulosum have occasional outgrowths of the stigmatic surface, which if not carefully inspected as high magnification [and particularly if the style is loaded with pollen] can appear as style branches.
Epilobium oreganum has truly 4-branched styles (see topmost photo above) and slightly zygomorphic flowers, features which you can readily see in the photo. My photo in Calphotos (0000 0000 0704 0293 (2004-07-11), the lowermost photo above, is E.glandulosum var. glandulosum: these plants had styles which are truly clavate with non-zygomorphic flowers, but the styles have warty outgrowths that could be confused with style branches. The 4-branched style condition in Epilobium shared only by other very distinctive species (E. luteum, E. niveum E. obcordatum, key couplet 14. in the Jepson Key).
So, it is my position that Oregon fireweed (Epilobium oreganum) does not occur in the Sierra Nevada, and that it is possible to mistake plants of E. glandulosum var. glandulosum that have warty outgrowths on the style as having branched styles, and thus misapply the name Epilobium oreganum.
Epilobium oreganum is a narrow endemic of the Klamath Region in Del Norte Glenn, Humboldt, Mendocino, Shasta, Siskiyou, Tehama and Trinity counites in California, and Josaphine, Jackson and Douglas counites, Oregon.