Key to Wisconsin Thelypteris

• 1a.Blades greatly narrowed toward the base, lowest 2--4 pinnae less than 1/4 as long as middle pinnae; petiole shorter than the blade T. noveboracensis

• 1b.Blades slightly narrowed toward base, lowest few pinnae at least half as long as middle pinnae; petiole as long or longer than the blade 2

• 2a.Most veins of sterile lobes forked before ending at margin; margins of fertile segments rolled under; indusia without glands T. palustris

• 2b.All veins of sterile lobes straight, unforked to the margin; margins of fertile segments flat; indusia with minute glands T. simulata