Thelypteris palustris is a fern from a slender, creeping rhizome, colonial.
Leaves arising singly along the rhizome; to 80 cm long, stalk to 35 cm long, on sterile leaves, to 70 cm on fertile leaves (longer than blade), black at base, smooth; blade to 40 cm long, 20 cm wide, tip tapered, base slightly narrowed, once pinnate-pinnately lobed, leaflets (pinnae) to 2 cm wide, lobed almost to leaflet midrib, lobes, to 1 cm long, 0.5 cm wide, midribs and veins hairy, margin smooth (entire); fertile lobes with margins curled inward.
Spore cases numerous, on upper leaflets of fertile fronds near midrib, eventually back of leaflet becoming brown with ripening sori.
Wetland status: FACW+.
Frequency in NYC: Infrequent.
Origin: Native to NYC.
Habitat: Open marshes, pond edges, wet soil. Not very tolerant of shade.