Shield Fern family (Dryopteridaceae)
Description: This native perennial fern consists of several ascending leaves about 6-12" tall; the leaves are usually organized together in a loose spreading clump. The leaf blades are 4-10" long and about 1/2 to 1/3 as much across; in overall shape, they are ovate or deltoid-ovate and broadest toward the middle or near the base. The structure of each leaf blade is bipinnate-pinnatifid or pinnate-bipinnatid the leaflets and their lobes tend to be less differentiated toward the tip of the leaf blade than at its base. There are about 8-12 pairs of leaflets along the rachis (central stalk) of each leaf; the leaflets are not necessarily opposite from each other. Each leaflet is lanceolate or deltoid-lanceolate in its overall shape. The ovate or oval lobes of the leaflets are pinnatifid, crenate, and/or shallowly cleft along their margins.
The surface of the leaf blade is hairless and slightly membranous; the abundant veins terminate near the tips of the leaflet lobes, rather than their sinuses. The slender leaf petioles are as long or shorter than the leaf blades; they are light green or yellowish green and hairless. The sori (spore-bearing structures) are located on the leaf undersides; they are arranged in small groups near the margins of the leaf lobes. Each sorus is round in shape; it has an indusium (pale membrane) that is 0.5 mm. across. The indusium soon fades away and becomes obscured by the brownish sporangia containing the spores, which are released during the summer. Each spore is about 30 micrometers across; it is brown, globoid, and prickly. Distribution of the spores is by wind. The root system consists of long hairy rhizomes, from which the leaves develop.
Cultivation: The preference is light shade, moist to slightly dry conditions, and a loamy or rocky soil with abundant organic matter. This little fern is reportedly easy to grow in shaded situations if taller vegetation is kept away from it.
Range & Habitat: The Fragile Fern occurs in every county of Illinois and is rather common. Habitats include moist to dry deciduous woodlands (both Sugar-Basswood or Oak-hickory), wooded bluffs, shady riverbanks, and areas along cliffs. It often found growing along gentle slopes, near the tops of ravines, or the edges of bluffs, where the ground vegetation during the summer is rather sparse.
Faunal Associations: The foliage of this small deciduous fern has little value to wildlife. Some upland gamebirds (Wild Turkey, Ruffed Grouse) and the White-Tailed Deer may eat the fronds to a limited extent.
Photographic Location: A deciduous woodland at Busey Woods in Urbana, Illinois.
Comments: The Fragile Fern is probably the most common fern in Illinois. It is still referred to as Cystopteris fragilis var. protusa in many older texts, but is now considered a separate species. Other closely related ferns in this genus are Cystopteris fragilis (formerly Cystopteris fragilis var. fragilis) and Cystopteris tenuis (formerly Cystopteris fragilis var. mackayi), which are uncommon in Illinois. These species have rhizomes that are short and scaly, while those of Cystopteris protrusa are longer and more hairy-looking. They are also more likely to have petioles that are brown in lower half, while the petioles of Cystopteris protrusa are usually yellowish green throughout. The veins of Cystopteris protusa usually terminate near the tips of the leaflet lobes, while the veins of other Cystopteris spp. in Illinois are more likely to terminate near the sinuses of the leaflet lobes.