Thelypteris palustris

Thelypteris palustris, the marsh fern, or eastern marsh fern, is a species of fern native to eastern North America and across Eurasia. It prefers to grow in swamps, bogs, wet fields or thickets, fresh tidal and nontidal marshes, or wooded streambanks. The species epithet palustris is Latin for "of the marsh" and indicates its common habitat. It is the only known host plant for Fagitana littera, the marsh fern moth.

Description
Fronds of T.palustris are erect to ascending with an elliptic to lanceolate form. They are 1-2.5 ft long and 4-7 inches across and have 10-40 pairs of leaflets. Its leaves are pinnately lobed, with the middle pinna being the widest. The leaves are more than 6 inches long, and the 3-6 inches wide. Sori are present on the undersides of the smaller fertile leaves.

The stem is tan to purplish and hairless.

Uses
T.palustris has been studied for potential uses in phytoremediation. T.palustris has been shown to significantly reduce the amount of Zn2+ and Cu2+, which are the main outputs of heavy metal from intensive livestock production, ex situ. There have been mixed results for whether T.palustris would be a good candidate for remediation of arsenic soil contamination.

Subtaxa
The following subspecies are accepted:
 * Thelypteris palustris subsp. palustris
 * Thelypteris palustris subsp. pubescens (G.Lawson) Fraser-Jenk.