Leaves and stems:

Leaves (fronds) are mostly erect, 2 to 10 inches long, up to 5 inches wide, narrowly lance-elliptic in outline, broadest near the middle, usually twice compound with 6 to 15 pairs of opposite leaflets (pinnae). Pinnae are mostly lance-oblong to narrowly triangular in outline. The largest leaflets have 3 to 9 pairs of lobes, lance-oval with a rounded or blunt tip; edges are minutely toothed and sometimes shallowly lobed.

Veins are unbranched, branched or forked, mostly obscure except for an enlarged pore (hydathode) near the vein tip which is most easily seen on the upper surface but is often also obscure. Both surfaces are sparsely to moderately covered in glandular hairs, more densely so on the underside, and lack any non-glandular hairs or scales.

The lower stem (stipe) is dark purplish to reddish-brown, covered in scattered brown scales, some with a darker stripe down the middle, and has sparse glandular hairs near the frond. The upper stem (rachis) is grooved, green to straw-colored at least towards the tip, has scattered hair-like scales, and is sparsely to moderately glandular hairy all over. Plants form a tight clump, the old stem bases persisting to the next year, broken off at varying points so are of varying lengths.

Spores:

The sori (group of spores) develop on the underside of fertile fronds starting in early to midsummer. They are circular and arranged in a row between the midrib and the edge of a pinna lobe. Spores mature to dark brown. Surrounding the sori is short, hair-like tissue (indusium). There is no visual difference between fertile and sterile fronds.

Notes:

Oregon Woodsia is one of 6 Woodsia species in Minnesota, most often found on bedrock outcrops, talus slopes, and in the cracks and crevices of cliffs and bluffs, mostly in the Minnesota River Valley and along the Canadian shield in the arrowhead region. According to the DNR, these habitats are at risk particularly from mining. Woodsia oregana was listed as a Special Concern species in 2013, and is also Special Concern in Wisconsin.

Oregon Woodsia is distinguished from the other Woodsia ferns by its stems that are dark at the base, green to straw-colored above and lack a joint near the base, persistent old stem bases of varying lengths, short hair-like indusia that surrounds the sori, and sparsely to moderately covered all over with short glandular hairs, no non-glandular hairs, and a few hair-like scales. Most similar are Blunt-lobed Woodsia (Woodsia obtusa), which has indusia with broader lobes and not hair-like, and Rocky Mountain Woodsia (Woodsia scopulina), which has a stem reddish-brown at the base covered all over in a mix of short glandular and longer multi-cellular hairs. Other Woodsia species may have jointed stems with old stem bases of equal lengths, have once compound leaves, a more densely scaly rachis, have non-glandular hairs and/or lack glandular hairs.

W. oregana is one Woodsia resembling Cystopteris ferns, which also mostly grow on rocks, but Cystopteris ferns lack the enlarged pore (hydathode) at vein tips (a distinctive trait of Woodsia), lack persistent stem bases, and most lack glandular hairs. There are 2 recognized subspecies of W. oregana: subsp. oregana is a western species with smaller spores (measure in micrometers) and the pinnae lobe edges are smooth; subsp. cathcartiana is as described above and the more common of the two. Our subsp. is named after Miss E. W. Cathcart, a botanizer from St. Paul who collected the first specimens in Taylors Falls and Duluth in 1896. For a time it was thought the Minnesota/Wisconsin border region was the only location for subsp. cathcartiana, but it was later found to be more widely established than subsp. oregana.