Gymnocarpium jessoense is a rare fern, similar in appearance
to the common G. dryopteris. Fronds are usually less than
40 cm long. The blade ranges from 3-14 cm long and is shorter
than the stipe. The blade is broadly triangular, 2- pinnate-pinnatifid
and ternate (divided into three roughly equal branches at the
base). Sori are round, located on the underside of the blade and
there is no indusium. The horizontal stems are elongate so leaves
are not densely aggregated.
There are three similar species in this genus in Wisconsin, distinguished
as follows. The abaxial (under) surface of rachis and blade of
G. jessoense are clearly glandular and the adaxial (upper)
surface is glabrous. G. dryopteris is glabrous on both
surfaces and G. robertiana is glandular on both surfaces.
Basal pinnae of G. jessoense are often curved toward
the tip of the frond, and those of G. robertianum are usually
straight and not pointing toward the tip of the frond. The reader
is directed to the Flora of North America, upon which this description
G. jessoense is found primarily from Wisconsin, Minnesota
and Ontario, west through Canada to Alaska. Disjunct locations
are also known from eastern Canada and the northeastern U.S. It
is listed as a "special concern" species in Wisconsin
where it has been recorded only from Bayfield County, often on
or near acidic rocks.