Leaves and stems:

Leaves (fronds) are once compound, lance-elliptic in outline, widest near the middle, narrowed at the base with a long taper at the tip end, 18 to 40 inches long, 5 to 10 inches wide, with 20 to 25 pairs of leaflets (pinnae) alternately attached along the stem. Pinnae are generally oblong in outline with a pointed tip, deeply lobed not quite to the midrib, the lobes abruptly reduced in size at the tip of the pinnae. The lowest pinnae typically point downward.

Lobes are short oblong, rounded or squared at the tip and shallowly toothed to toothless around the edge. Surfaces are sparsely hairy, veins are free and not forked. The central stalk of the pinnae is variously covered in silvery hairs, especially on the underside.

The central stem (stipe) is grooved, reddish brown at the base, becoming straw-colored above, and is densely covered in silvery hairs all along its length. The plant grows in an asymmetrical clump, the fronds spreading in all directions. Colonies may form from short creeping rhizomes.

Spores:

The sori (group of spores) are found on the underside of the pinnae and mature in mid to late summer. Sori are linear-oblong and straight or hooked at the tip and run along the veins of the pinnae lobes, creating a herringbone pattern on the lobes. A linear tissue (indusium) partly covers the spores and is initially silvery white then turns brown. Spores ripen from brown to blue-gray. Fertile fronds may be slightly taller and narrower than sterile fronds but, except for the presence of sori, are otherwise the same.

Notes:

At first glance, Silvery Spleenwort may be mistaken for Lady Fern (Athyrium filix-femina), which is twice compound with distinctly separate segments on leaflets. The deeply lobed pinnae also somewhat resemble those of Cinnamon Fern (Osmundastrum cinnamomeum) and Interrupted Fern (Osmunda claytoniana), both of which have sori on separate structures, not on the pinnae. Silvery Spleenwort's densely hairy stipe also distinguishes it from other ferns. The name “spleenwort” is a bit of a misnomer, a holdover from a time this species was included in Asplenium. Older references list it as the synonym Athyrium thelypteroides, and for a brief time it was known as Diplazium acrostichoides. Such is the way of taxonomy. Minnesota's southeast counties are at the northwest tip of its range and, according to the DNR, its woodland and bluffland habitats are at risk from development, logging, and livestock grazing, all of which increase the risk of further degradation from invasive species. Silvery Spleenwort was listed as a Special Concern species in 2013.