No, mine's not ferny. It's just like the photo in the first post, and in Kent's link. It's just a tallish, leafy nothing-to-speak-of plant. It fools me until it's bigger because until the top gets that droopy-plumey look, it sort of resembles perennial phlox leaves.
Roots on this plant are mostly close to the surface, but break off easily. It's difficult to eradicate without digging up and re-setting the phlox. Even then the roots of the phlox have to be washed enough to check for little pieces of Mare's Tail roots. Ugh!
Thanks for the ID, Kent!