Polystichum

1. Blades fully 2-pinnate.

P. braunii

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.

P. acrostichoides

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.

P. lonchitis

All species found in Polystichum

Polystichum acrostichoidesCHRISTMAS FERN 
Polystichum brauniiBRAUN'S HOLLY-FERN 
Polystichum lonchitisNORTHERN HOLLY-FERN 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. October 19, 2017. http://michiganflora.net/genus.aspx?id=Polystichum.