The word in the original song is 'aronatus,' which cannot be found or identified from any of the floras of the region, nor from lists of any cultivated flowers. Was it mis-heard 'aromaticus,' Arenaria (related to Dianthus, or pinks),' 'armatus'?
We will never know unless Maud Irving can be resurrected from the dead.
The song says that the flower is pale with eyes of bright blue. This is the only clue.

In the original song, the "frail wildwood flower" is the singer herself, not a flower in the botanical sense.