Leaves and stems:

Leaves are once compound, 6 to 30 inches long and 3 to 7 inches wide, lanceolate shaped in outline, the lowest leaflets at least half as long as the longest ones below the middle of the leaf. Leaf surfaces are typically hairless though the leaflet mid-nerve is slightly hairy. Leaves are mostly erect, growing in a random pattern from creeping rhizomes.

Leaflets are light green, deeply lobed, divided almost to mid-nerve, the lobes up to ¾-inch long, oblong to triangular, toothless with a blunt to pointed tip. Veins extend to the edge of the lobe and are mostly forked, though fertile leaves have some unforked veins.

The base of the stem is smooth and dark brown to black with a few scattered small tan scales. The upper stem is slightly hairy and green to straw-colored, sometimes with a few scattered scales.

Spores:

Spores mature in mid to late summer, appearing on the back of fertile leaves, which are more erect, taller and narrower than the infertile leaves. The sori (group of spores) are round and covered by tissue (indusium). The sori are in a row on both sides of the lobe midvein, the sori attached on the veins. The leaf edges slightly roll under, slightly covering the sori.

Notes:

This is a common fern of wet sunny places, though it does tolerate light shade and is not typically found in standing water. A non-clumping fern, it often forms colonies from its long creeping rhizomes. Flora of North America notes 2 varieties in North America; var. pubescens is found in Minnesota as well as about 2/3 of the rest of North America. Northern Marsh Fern may look similar to Lady Fern (Athyrium Filix-femina) but Lady Fern grows in clumps and has distinctly toothed leaflets.