Jennifer, I think you've found the answer. Stipa brachytricha was discovered to be a synonym for Calamagrostis brachytricha long ago -- so long ago that the taxonomic databases no longer bother to include the Stipa name in their listings. Calamagrostis brachytricha, in turn, became a synonym for Calamagrostis arundinacea. We have entries for all three names, so I'll merge them. Thank you.
I guess it's time to update the grasses in our database.