Thelypteris palustris (Northern Marsh Fern)
|Also known as:||Eastern Marsh Fern|
|Family:||Thelypteridaceae (Marsh Fern)|
|Habitat:||part shade, sun; bogs, marshes, wet meadows, seeps, fens, along shores|
|Plant height:||6 to 30 inches|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: FACW|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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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.
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.
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.
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Photos by K. Chayka taken at Cedar Creek Natural History Center, Battle Creek Regional Park, and Blaine Preserve SNA. Photos courtesy Peter M. Dziuk taken in Anoka County.
Have you seen this plant in Minnesota, or have any other comments about it?