northwestern lady fern

(Athyrium filix-femina var. cyclosorum)

Conservation Status


No image available

  IUCN Red List

not listed


NNR - Unranked


not listed

Wetland Indicator Status
  Great Plains

FAC - Facultative


Northwestern lady fern is a relatively large, delicate, perennial fern that rises from a short-creeping rhizome and fibrous roots. The rhizome is sometimes semi-erect and often branched. It usually has the bases of dead stalks still attached. It often forms small colonies.

Sterile and fertile fronds are similar in appearance. The fronds are deciduous, erect, arching, 11½ to 36 long, and lacy in appearance. They form a compact, somewhat circular but irregular cluster.

The leaf stem (stipe) is 6 to 17¾ long, shorter than the leafy portion (blade). It is stout and light green or straw-colored for most of its length. It is flattened at the base and becomes deeply grooved toward the top. At the base it is dark reddish-brown or black, swollen, and has 2 rows of teeth. The stipe is covered with scattered chaffy scales. The scales are brown or dark brown, lance-shaped or egg lance-shaped, to ¾ long, and 1 16 to 3 16 wide.

The blade is elliptic to inversely lance-shaped, 12 to 30 long, 4 to 14 wide, about 2 times as long as the stipe. It is pinnately divided into 30 to 40 pairs of leaflets (pinnae). It tapers to a point with concave sides along the tip, and is widest below the middle. The 4th or 5th pair of pinnae is the largest pair. Only the lowest two pair are shortened. The lowest pair is conspicuously angled downward. The central axis of the blade (rachis) is pale green and usually hairless, sometimes sparsely glandular or hairy, sometimes with a few scattered scales.

The pinnae are oblong lance-shaped, short stalked or stalkless, and taper to a narrow point with concave sides along the tip. The longest pinnae are up to 8 long or longer, becoming shorter as they approach the tip. They are deeply, pinnately divided, with 12 to 20 segments (pinnules) per side.

The pinnules are variable. They are linear to oblong, angled at the tip, and asymmetrically wedge-shaped at the base. They are stalkless and may extend along the central axis of the pinna (costa) at the base. They are often deeply lobed (pinnatifid), cut up to halfway or more to the midrib (costule). The upper and lower surfaces are medium green to yellow-green and hairless. The veins visible on the underside are forked. They are free, meaning they do not rejoin but extend all the way to the margin. The margins are minutely toothed, tough, and firm, but elastic.

The rachis, costa, and costule have a V-shaped groove on the top. The groove of the costule connects with the groove of the costa, which connects to the groove of the rachis, which connects to the groove of the stipe.

The reproductive structures are born on the underside of the pinnules near the base. There are several clusters (sora) of spore-bearing cases (sporangia) arranged in one row on each side of the midrib halfway between the midrib and the margin. The sorus is hooked at the end or horseshoe-shaped with the hook curled over a vein. It is covered with a protective veil (indusium). The indusium is the same shape as the sorus. It is irregularly toothed and has a fringe of long hairs along the margin. The hairs are as longer or longer than the indusium is wide. The indusium is attached to one side of the sorus.

There are 64 yellow spores per sporangium.




Fronds 11½ to 36 long


Similar Species


Common wood fern (Dryopteris intermedia) fronds are evergreen, not deciduous. The sori are round. The indusia are kidney-shaped and are attached at the base of the notch.

Northern lady fern (Athyrium filix-femina var. angustum) scales on the stipe are much smaller, no more than long, and 1 16 wide. The blade is 1 to 1½ times as long as the stipe and broadest below the middle. The 4th or 5th pair of pinnae is the largest pair. The sorus is usually straight, sometimes hooked or horseshoe-shaped. The indusium has a fringe of shorter hairs along the margin. The spores may be yellow or brown.

Spinulose wood fern (Dryopteris carthusiana) fronds are evergreen, not deciduous, and are usually smaller, no more than 30 long. The sori are round. The indusia are kidney-shaped and are attached at the base of the notch.


Moist. Bottomland forests, moist woods, meadows, thickets, swamps, streambanks. Dappled sunlight to light shade.




July to October




Distribution Map



3, 4, 29, 30.








Rare or absent in Minnesota

There is just one report of northwestern lady fern in Minnesota. It is from the Bell Museum of Natural History in Minneapolis. That record has no date or location information.

  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Polypodiophytina  
  Class Polypodiopsida (ferns)  
  Subclass Polypodiidae  


Polypodiales (true ferns)  




Athyriaceae (lady ferns and allies)  


Athyrium (lady ferns)  


Athyrium filix-femina  

The genus Athyrium was formerly placed with the spleenworts in the family Aspleniaceae. Today, most place it in the new family of lady ferns and allies, Athyriaceae. Some taxonomists, including ITIS, place it with the cliff ferns in the family Woodsiaceae. However, the more broadly defined Woodsiaceae would be invalid (paraphyletic). Some taxonomists, including Flora of North America and USDA PLANTS, place the genus with the wood ferns in the family Dryopteridaceae. Neither classification is widely accepted.

Most sources list northern lady fern as a variety, Athyrium filix-femina var. angustum. iNaturalist and USDA Plants list it a subspecies, Athyrium filix-femina ssp. angustum. Some list it as a separate species, Athyrium angustum.




Athyrium alpestre var. cyclosorum

Athyrium angustum var. boreale

Athyrium angustum var. borealis

Athyrium angustum var. elatius

Athyrium filix-femina ssp. cyclosorum

Athyrium filix-femina var. sitchense


Common Names


northwestern lady fern

subarctic ladyfern










The central axis of a pinna, to which pinnules are attached.



The midrib of a pinnule.



A large leaf with many divisions: in ferns, the compound leaf, including the stipe and the blade; in mosses, a closely and regularly branched stem resembling a fern leaf; in lichens, a stalkless, leaf-like extension.



Undergarment. In ferns: A veil covering the cluster (sorus) of spore-producing structures (sporangia). In fungi: A skirt-like structure hanging from the cap (receptacle) of a stinkhorn.



Long, straight, and narrow, with more or less parallel sides, like a blade of grass.



The primary division of a compound leaf or fern frond.



Having the leaflets of a compound leaf arranged on opposite sides of a common stalk.



Deeply cut, more than half way to the midrib but not to the midrib, into lobes that are spaced out along the midrib; the lobes do not form separate leaflets.



The ultimate segment (individual leaflets) of a twice or more compound leaf or fern frond.



The main axis of a compound leaf, appearing as an extension of the leaf stalk; the main axis of an inflorescence.



A horizontal, usually underground stem. It serves as a reproductive structure, producing roots below and shoots above at the nodes.



A compact cluster of spore-bearing cases or sacs (sporangia) on a fern.



A spore bearing structure, as of a fern or moss.



A supporting stalk-like structure lacking vascular tissue: in fungi, the stalk supporting the mushroom cap; in ferns, the stalk connecting the blade to the rhizome; in flowering plants, the stalk connecting the flower’s ovary to the receptacle; in orchids; the band connecting the pollina with the viscidium.

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