Description: This native perennial fern produces evergreen leaves up to 10" long and 3" across on naked stalks; these arching leaves occur individually or in small loose clumps. Each leaf is lanceolate-oblong or elliptic-oblong in overall shape; its structure is deeply pinnatifid with about 10-22 pairs of lobes along the central vein. These lobes are longest toward the lower middle of each leaf, becoming gradually smaller until they merge into a terminal lobe that is triangular-shaped. The upper surface of each leaf is medium to dark green with a lustrous appearance, while the lower surface is light green and hairless. The non-terminal lobes of each leaf are oblong or lanceolate-oblong in shape; they are smooth, slightly undulate, or minutely toothed along the margins. The sinus (or cavity) between each pair of adjacent lobes is cleft, rather than rounded; because the pairs of opposite lobes are asymmetrically aligned, this creates a characteristic zigzag pattern along the central midvein of each leaf. Each lobe also has a prominent central vein. The stalk at the base of each leaf is up to 5" long, light green, and glabrous; the central midvein of each leaf is also light green and glabrous.
The sori (or spore-bearing structures)
are located on the underside of the leaves. There are about 4-10 pairs of sori
on either side of the central vein of each lobe; they are located about
half-way between the central vein and each margin. Only the upper to middle
lobes have sori. The sori are round in shape and become orange-brown to brown
when they mature. Unlike many other species of ferns, the sori of Common
Polypody lack indusia (protective membranes). The spores are released during
the fall. The root system consists of long scaly rhizomes and fibrous roots. In
favorable habitats, large colonies of plants are occasionally
found.
Cultivation: This fern
prefers medium to light shade, thin rocky soil with an acid pH, and moist to
mesic conditions with high humidity levels. It also prefers sheltered areas
where there is some protection from the wind.
Range & Habitat: Common Polypody is occasional
in southern Illinois, uncommon in northern Illinois, and largely absent from
the central portion of the state (see
Distribution
Map). Habitats include shaded cliffs, rocky wooded bluffs, and shaded
sandstone ravines. In Illinois, this fern is usually found in sandstone-related
habitats.
Faunal
Associations: In general, the ecological value of this and other
ferns to wildlife is low. During the winter, when food supplies are more
limited, the Ruffed Grouse, Wild Turkey, and White-Tailed Deer eat the fronds
(or leaves) of various evergreen ferns to a limited extent.
Photographic Location: A sandstone ravine at the
Fall Creek Gorge (aka "The Potholes") in west-central Indiana.
Comments: The evergreen leaves of this fern are
quite attractive. It can be distinguished from other ferns by its pinnatifid
leaves, glabrous stems, and round sori that lack indusia (spore-bearing
structures without protective membranes). Another species in the Polypody
family, Pleopeltis polypodioides (Gray Polypody), is found only in
southern Illinois. Unlike Common Polypody, this latter species has scaly stalks
and scaly leaf undersides. Furthermore, its pinnatifid leaves have sinuses that
are rounded, rather than cleft. Sometimes Common Polypody is considered a
variety of the European species, Polypodium
vulgare.