Lady Fern, ATHYRIUM FILIX-FEMINA

from the August 16, 2009 Newsletter, reporting on a visit to Rogue River National Forest in southwestern Oregon:
NORTHWESTERN LADY FERNS
During my hike along the Rogue, when the trail dipped into a moist, shady little valley and a different fern species suddenly showed up, lots of knee-high, frilly ones, I was tickled. You can see one above.

*UPDATE: Years later ferns like these usually were assigned variety status, and known as Athyrium felix-femina var. cyclosorum. Then later that variety was raised to species level, so as of 2024 its name usually is given as ATHYRIUM CYCLOSORUM, and sometimes known as Northwestern Lady Ferns. As such, the species is said to be native from far eastern Russia across subarctic America into the western and central US. Other varieties of the formerly unified Lady Fern species similarly have been split up and have different names.

I knew this one from back in Kentucky. It's the Lady Fern, ATHYRIUM FILIX-FEMINA*, one of the most common and best known ferns species throughout the temperate zones of both North America and Eurasia -- it's "circumboreal." Among its field marks are the way its lower divisions, or pinnae, are much smaller than at the frond's middle. Also, look at the frond underside below:

In that picture, one feature confirming that it's a Lady Fern is that the veins DON'T reach the pinna's margin. Another feature is the special shape of each cluster of tiny, black spheres. Each of those clusters is a fruit-dot or sorus. The tiny, black spheres making up the sori are stalked, baglike sporangia. When a sporangium matures it bursts and releases spores, which under perfect conditions germinate to form tiny, flat things called prothalli (singular prothallus), the first stage of a fern's life cycle.

The sori are "kidney-shaped," or "reniform." Earlier they'd been covered with cellophane-like indusia, and each indusium had been attached by one side, not in the center, umbrella-like, as with the swordferns. You might enjoy comparing the Lady Fern's sori with those of our abundant swordferns at https://www.backyardnature.net/n/09/090503sg.jpg.