Marginal Shield Fern
Dryopteridaceae (Shield Fern family)
Description: This native perennial fern produces a rosette of ascending to arching evergreen leaves from a vertical rootstock. Each leaf is about 12½' long and 4-9" across (excluding its stalk); it is lanceolate-ovate in outline, while its structure is mostly bipinnate. Each leaf has 12-20 pairs of leaflets along its rachis (midrib); these leaflets are longest toward the lower middle or middle of the leaf. The tip of each leaf is rather long and slender, where the leaflets are reduced to small lobes. Each leaflet has about 8-15 pairs of short subleaflets. Each subleaflet is oblong or lanceolate-oblong in shape, shallowly cleft, and crenate along its margins; it has a blunt tip. The upper surface of each leaf is medium green and hairless; the lower surface is light green and hairless. The slender stalk of each leaf is about 3-10" long and light green or pale reddish-green; at least the lower half of the stalk is scaly, otherwise it is glabrous. The rachis of the leaf is light green and usually lack scales. Both the leaves and their leaflets can be straight, or they may curve gently in one direction or another.
The sori (spore-bearing structures) develop on the undersides of the leaves; they are located along the margins of the subleaflets. A subleaflet can have 3-6 sori along each of its margins. These small sori are orange-brown to brown and round in shape; each sorus has an indusium (protective membrane) that is anchored above its center. Eventually, this indusium withers away so that the sorus can release its spores. This usually occurs during the late summer or the fall. The root system consists of stout scaly rhizomes with fibrous roots. Vegetative colonies of plants are occasionally formed.
Cultivation: The preference is medium to light shade, mesic conditions, and a thin rocky soil with an acid pH. This fern prefers a location with high humidity that is protected from harsh winds.
Range & Habitat: The Marginal Shield Fern is common in southern Illinois, and occasional to rare elsewhere in the state (see Distribution Map). Habitats include rocky woodlands, rocky wooded slopes, sandstone ravines, and wooded slopes of stabilized sand dunes. This fern is often found in areas where sandstone is exposed to the ground surface; it is especially common in the Shawnee Hills of southern Illinois.
Faunal Associations: Little is known about the floral-faunal relationships for this species. The foliage of this fern is toxic and it is rarely browsed by White-Tailed Deer. Both the rhizomes and leaves are toxic to humans and can cause a variety of unpleasant symptoms, including death. In the past, the dried rhizomes of this and similar ferns (e.g., Dryopteris filix-mas) were used to expel tapeworms from the digestive tract, but today there are safer medications that can be prescribed for this purpose.
Photographic Location: A sandstone ravine at Fall Creek Gorge (aka "The Potholes") in west-central Indiana.
Comments: This medium-large fern has elegantly shaped evergreen fronds. Because it has a fairly conventional appearance for a fern, it may not be easy to identify at first glance. The most distinctive trait of the Marginal Shield Fern is the location of its sori: they can be found along the margins of its subleaflets. During the late spring or early summer, immature sori will look like small green bumps along the margins; later in the year, they become orange-brown and are much more conspicuous. In Illinois, other species in the Shield Fern family have their sori closer to the central vein of each subleaflet. Other common names of Dryopteris marginalis include Marginal Wood Fern and Leather Fern; the latter name refers to the texture of its leaves.