Etymology Palustris means marshy or swampy.

Description Rhizome: long-creeping, branching, black behind a white tip, 2.5 mm diam., cordate scales.
Frond: 75 cm high by 20 cm wide, deciduous, monomorphic, though sterile fronds are earlier, fertile narrower, taller, 6 weeks later, blade/stipe ratio: 1:1 to 3:1.
Stipe: straw-colored or darker, shading to green, a few scales near the base, vascular bundles: 2, oblong, at 90°, at stipe base, merging above to an open u-shape.
Blade: 1-pinnate-pinnatifid, lanceolate, widely separated pinnae, tapering to the tip, widest below the middle, narrowing somewhat to the lowest pinna, membranous, pale green, short, whitish hairs, falling soon, and yellow glands.
Pinnae: 14 to 20 pair, lanceolate, long tapering, less incised near the ends, 2 cm wide; costae grooved above, discontinuous with the rachis; margins sterile: entire to slightly toothed, fertile: narrower, triangular, folded downward; veins free, once-forked.
Sori: round, midway between the margin than the costule, merging into each other, indusium: small, irregular or somewhat reniform, shedding soon, maturity: mid to late summer.

Culture Habitat: swamps, bogs, and marshes, also along riverbanks and roadside ditches, and in wet woods . Distribution: Europe and northern Africa, western and central Asia, China; var. pubescens eastern North America, Bermuda, Cuba, Japan, northeastern Asia; var. squamigera in New Zealand. Hardy to -35°C, USDA Zone 3.

Distinctive Characteristics The long-running rhizome separates this from many ferns, the wide lowest pinnae pair distinguishes this from T. noveboracensis, and the 1-pinnate-pinnatifid division here from Dennstaedtia punctilobula.

Synonyms
Acrostichum thelypteris L
Polypodium palustre Salisb.
Lastrea thelypteris (L.) Bory
Thelypteris thelypteroides (Michaux) Holub
Dryopteris thelypteris (L.) Gray var. pubescens (Lawson) Nakai