The agony and the ectasy

It's always nice to find something new, and I was happy to see this little chap growing out of a hidden-away bridge, especially since I have done so poorly for ferns.

Naturally, things aren't that simple and after 2 days with Poland and Frey I still don't know what it is!

in situ

form

2 vascular bundles in petiole, not merged

vb

leaf detail

Poland
B. Ferns
   lvs 2-pinnate
   lvs opaque
   petiole w 2 vbs -> BG

BG.
   lvs < 1m
   pinnules with main vein present
   lowest pair of pinnae longest
   pinnae alternate, curving to apex
  ...