This is an attractive medium-sized fern with light green leaves. It is unusual among ferns because of its preference for sunny habitats. To identify this species, look for the strongly involute margins of the lobes and the forked lateral veins on their undersides. While it is not immediately obvious, the undersides of the central stalks (rachis) and lateral stalks (rachillae) are finely pubescent, rather than glabrous, for the North American ecotype of this fern. A similar species, Thelypteris noveboracensis (New York Fern), which is uncommon in Illinois, has lower leaflets that are substantially reduced in size. The lower leaflets of the Marsh Fern, in contrast, are only slightly reduced in size. Some authorities assign this fern to the Polypodiaceae (True Fern family); Dryopteris thelypteris is another scientific name for this species.