Good suggestion, Wim. But did many Danes die in the Vosges?? 
I must look to history, I think 
The Byzantine emperors in Constantinople had the Varangrian Guard which was made up of Scandanavians, Anglo-saxons and Russians so they (the Danes) traveled widely!
Also many of the known boats from Scandanavia at that period (early middle ages) have very shallow drafts which would have made them suitable for river travel as well as the open sea, so if the Vosages is anywhere near a major river system they may have made it there.
The alternative version of the legend is that the Danes planted it on the graves of their countrymen. Who might have died peacefully, in their beds, of old age, with their loving families around them.
The legend is suspiciously like a victorian invention - you know, lets recreate our myth of merrie olde england/scotland/wales etc and our valient defense against a nasty foe, real or imaginary. Sounds like a plant needing a legend . . .
Grieves' Herbal says it's called Hičble in french and Attichwurzel in german - no mention of dead danes there.
Sue
