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.