Woodsia ilvensis (Rusty Woodsia)
|Also known as:
|Rusty Cliff Fern
|Dryopteridaceae (Wood Fern)
|part shade, sun; dry; bedrock cliffs, outcrops, rocky slopes
|2 to 10 inches
|Wetland Indicator Status:
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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Leaves and stems:
Leaves (fronds) are erect to ascending, 2 to 10 inches long (typically 4 to 6), ½ to 1½ inches wide, narrowly lance-shaped in outline, broadest below the middle, once compound with 10 to 20 pairs of opposite leaflets (pinnae), the lowest pairs usually twice compound. Pinnae are lance to triangular in shape, lobed, toothless to scalloped around the edges, rounded or blunt at the tip, sparsely hairy on the upper surface, the lower surface covered in a mix of long white hairs and tan scales that turn rusty brown with maturity. The largest leaflets have 4 to 9 divisions. Veins are free and mostly forked, sometimes ending in a raised pore (hydathode) near the leaflet edge which is most easily seen on the upper surface.
Stems are initially green, covered in a mix of long, white hairs and linear, tan scales. The lower stem (stipe) turns dark purplish to brown and has a small, swollen node about halfway between the base and the lowest pinnae; the upper stem (rachis) is grooved and turns mostly rusty brown except at the very tip. Hairs and scales turn rusty brown with maturity. Plants form a tight, compact clump, the old stem bases persisting to the next year, broken off at the node and all more or less the same length.
Surrounding the sori are hair-like tissues (indusium) that are initially white and tightly wound into a ball, but unravel and turn brown as spores develop. The indusium often persists but may become obscure.
Of the 6 Woodsia species in Minnesota, this is the most common, found primarily along Lake Superior's rocky north shore, and the bedrock cliffs and outcrops of the Minnesota River Valley and Canadian Shield. It is easily distinguished from other ferns by its dense covering of long hairs and scales on the underside of pinnae, the largest pinnae with 4 to 9 divisions, and the persistent old stem bases all about the same length. Other Woodsia species lack the hairs and/or scales or are only sparsely covered, or have fewer divisions on the largest pinnae, or may have persistent stem bases of varying lengths. The only other fern in Minnesota of similar size and degree of hairiness is Slender Lip Fern (Myriopteris gracilis, formerly Cheilanthes feei), which is limited to a few southeast counties and has distinct, bead-like segments on pinnae.
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- Rusty Woodsia plant
- Rusty Woodsia plants
- Rusty Woodsia plants
- Rusty Woodsia habitat
- mature sori
- late season, after spores are released
- persistent old stem bases of similar length
Photos by K. Chayka taken in Cook County and at Split Rock Lighthouse State Park, Lake County. Photos by Peter M. Dziuk taken in Cook and Lake counties.
Have you seen this plant in Minnesota, or have any other comments about it?