Leaves and stems:

Leaves (fronds) are evergreen, 2 to 8 inches long, up to about ½ inch wide, linear in outline, widest at or above the middle, tapering at both ends, once-compound with 15 to 35 pairs of opposite leaflets (pinnae). Pinnae are oval-oblong, 1/8 to 1/3 inch long, nearly as wide, hairless, and scalloped around the edges. Veins are free, branching off an obscure midvein. The stem is dark purplish brown to nearly black and glossy for the entire length, with a few small, dark brown to black scales at base. Stems may persist after the pinnae fall off. Asymmetrical clumps form from a short rhizome.

Spores:

The sori (group of spores) are found on the underside of the pinnae and mature in mid-summer to fall. Sori are about 1mm long, linear-oblong, and run along the pinnae veins with 2 to 5 sori per pinna. A linear tissue (indusium) partly covers the spores and is initially white then turns brownish. Spores ripen from reddish to brown. There is no significant difference between sterile and fertile fronds, except sterile fronds emerge earlier and tend to be prostrate.

Notes:

Maidenhair Spleenwort is a small, delicate fern of cool, shady, forested cliffs and talus slopes. There are 2 subspecies: subsp. quadrivalens is found on calcareous rocks such as limestone and dolomite, and subsp. trichomanes is found on acid rocks such as sandstone and granite. According to the DNR, the one record from Goodhue County, collected in 1895, provided no habitat information but, considering the limestone and dolomite bedrock in the area, this was possibly subsp. quadrivalens, where the populations in northern Minnesota are all subsp. trichomanes. The Goodhue population was never found again so that is all speculation now. The remaining populations are small, in isolated and fragile habitats and are vulnerable to local extinctions. Maidenhair Spleenwort was listed as a Threatened species in 1984 and is a Special Concern species in Wisconsin. It is easily recognized from the asymmetrical clump of narrow fronds, the pinnae all opposite or nearly and not much longer than wide, and the oblong sori along the veins.