Diplazium pycnocarpon, formerly Athyrium pycnocarpon

Good call, Scott and John! Diplazium pycnocarpon it is, also known as Glade Fern or Narrow-leaved Spleenwort. In northern Indiana this exceedingly rare native grows in rich mesophytic woods, in deep humus and deep shade. It has a special affinity for those rich riparian bottoms that don't get scoured bare by filthy water gushing in torrents from denuded uplands every time it rains. Fertile blades are rare and emerge in late summer.

Henry David Thoreau said, "Nature made ferns for pure leaves, to show what she could do in that line." Well said, and noted!