1. Blades fully 2-pinnate.
1. Blades once-pinnate, the pinnae at most spiny-toothed (rarely, the lowermost pinnae pairs will have small lobes adjacent to the rachis).
2. Lowermost pair of pinnae narrowly elliptic, not strongly reduced in size; petioles, at least of larger leaves, 9–26 cm long; upper fertile portions of leaf with pinnae distinctly narrower and smaller than the sterile pinnae.
2. Lowermost pair of pinnae triangular, much smaller than the pinnae in the mid-leaf zone; petioles 2–8 cm long; fertile and sterile pinnae similar in size and shape.
All species found in Polystichum
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. July 22, 2019. https://www.michiganflora.net/genus.aspx?id=Polystichum.