Gymnocarpium

1. Rachis of blade and midveins on the underside of the pinnae glabrous; blades with the two basal segments nearly as large as the rest of the blade, the blade thus about as wide as long.

G. dryopteris

1. Rachis of blade and larger midveins on the underside of the pinnae finely glandular with delicate, short-stalked glands; the two basal segments clearly smaller than the rest of the blade, the blade thus usually longer than wide.

2. Blades glandular on the upper surface, especially on the midveins of the pinnae and adjacent to the rachis; lowermost (first) pinnae pair diverging at a right angle, not upward pointing; the second pinnae pair usually with a petiole.

G. robertianum

2. Blades glabrous on the upper surface; lowermost (first) pinnae pair usually clearly upwardly pointing; the second pinnae pair sessile.

G. jessoense

All species found in Gymnocarpium

Gymnocarpium dryopterisOAK FERN 
Gymnocarpium jessoenseNORTHERN OAK FERN 
Gymnocarpium robertianumLIMESTONE OAK FERN 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. July 25, 2017. http://michiganflora.net/genus.aspx?id=Gymnocarpium.