The stalks are usually but a few (four to six) inches long, and in the dried specimens of a brownish straw-color, becoming nearly black at the base. They bear a few large ferruginous chaffy scales, and are deeply channelled and furrowed. The fibro-vascular system of the stalk is altered by contraction in drying, but apparently agrees with Dr. Milde’s description of _Athyrium_: “There are two oblong peripheric bundles in the _base_ of the stalk, which, at the base of the lamina, are united into one of a horse-shoe shape by an arc parallel to the back of the stalk.” In the middle of a stalk from one of the California specimens I find two systems of ducts, one on each side of the stalk, and the two united by a curved and contorted border of firm blackish tissue (sclerenchyma).
The fronds are from one to two feet long, and from three to six inches wide. In general shape they are oblong-lanceolate, acuminate, and slightly narrowed at the base. The texture is softly membranaceous, and both surfaces are smooth. The primary pinnæ are numerous, the lower ones gradually farther apart: their shape is lanceolate from a broad base. They are usually twice pinnatifid, the pinnules being connected by a very narrow foliaceous border along the midribs. The ultimate segments are sharply toothed. The fruit-dots are very abundant, and usually are found on all the pinnæ. They are placed on the back of the free veinlets, and are apparently devoid of indusium; though Dr. Mettenius has discovered on young fronds an exceedingly delicate and fugitive indusium, resembling in some degree that of _Asplenium § Athyrium_. Accordingly, in his later work, he referred the species to the genus _Asplenium_, placing it next to _A. Filix-fœmina_. Milde, in his work on the ferns of Europe and Atlantis, sought to re-establish Athyrium as a genus, and placed this fern in it, saying “sori ... rotundi, primum breviter oblongi indusio fugaci minutissimo ciliato instructi.” The spores are ovoid, and apparently covered with anastomosing raised lines. Those I have examined are fuscous-brown, but Milde says “sub-nigræ verrucosæ.”
There is a European var. _flexilis_, with very narrow, nearly sessile fronds, and the pinnæ often deflexed, which has not been observed in America.