Both have been placed in the same species, Botrychium lanceolatum and assigned varietial names(some classify as subspecies). The Eastern variety is v. angustisegmentum and the Western natives become the autonym variety: v. lanceolatum.
The Flora of North America describes the two varieties as differing only in the width of about two of the middle segments: v. lanceolatum 2mm or more, v. angustisegmentum, 2mm or less.
After looking at several photos of v. angustisegmentum from different geographic areas(geotypes) of the Eastern US and comparing those with v. lanceolatum from the West Coast, I am wondering how the taxonomists determined which was the "normal" shape of either? Could be that the determination is based upon Herbarium specimens, which turns out to be slightly different.
Rb