A collection of Asplenium montanum purported to have come from the Keweenaw Peninsula exists, but Drife & Drife (1990) concluded that it is clearly the result of a labeling error.

1. Leaf entire.

2. Leaf apex long-tapering to a gradual point, rooting at the tip if in contact with soil or moss.

A. rhizophyllum

2. Leaf apex abruptly pointed to ± rounded, never tip rooting.

A. scolopendrium

1. Leaf pinnately compound.

3. Blades ovate in outline; pinnae only 3-5 per side.

A. ruta-muraria

3. Blades linear in outline, pinnae ca. 6-40 per side.

4. Rachis of larger leaves green for most of their length, pale brown only near the base.

A. viride

4. Rachis of larger leaves dark reddish brown to almost black for most of their length.

5. Pinnae with enlarged lobe on the upper side next to and usually overlapping the rachis; plants usually on soil.

A. platyneuron

5. Pinnae lacking an enlarged lobe, tapering nearly equally to the base; plants usually on rock.

A. trichomanes