Description: This native perennial fern develops an erect and rather stout stem about 2½' tall, from which there extends a single compound leaf about 3½' long and 3' across. In shady areas, the compound leaf usually extends horizontally in relation to the ground, while in sunny areas it is more ascending. The compound leaf varies in color from yellowish green to medium green. The compound leaf has an irregular structure; it is mostly bipinnate-pinnatifid and, to a lesser extent, ternately pinnate (3-pinnate). Each compound leaf is divided into 3 major branches (1 central, 2 lateral). A single branch of the compound leaf has a pinnate-pinnatifid or bipinnate structure; it is triangular in outline. The rachis of each branch is light green and hairless (or nearly so). There are about 12 pairs of leaflets along the central axis (rachis) of each branch; the leaflets toward the base of the branch are much longer than the leaflets toward its tip. The leaflets toward the base are more likely to be odd-pinnate, while the leaflets toward the tip are more likely to be odd-pinnatifid. Individual leaflets have 1-15 pairs of subleaflets or lobes; they are usually oblong in shape. The terminal lobes (or subleaflets) are elongated in shape and finger-like in appearance; they are 3-6 mm. (1/8–1/4") across and 2-4 times longer than wide. The margins of the subleaflets and lobes are smooth and sometimes slightly undulate; they bend downward.
The reproductive structures (indusia,
sporangia) are located along these rolled margins on the underside of the
compound leaf. These reproductive structures are produced sparingly; when they
occur, the spores are usually released during summer or fall. The root system
system is fibrous and rhizomatous; individuals rhizomes can extend many yards
(or meters), sending up new vegetative shoots every 1-5 feet. As a result,
sizable colonies of plants are fairly common. The growing tips of rhizomes are
either glabrous or sparsely white hairy. The compound leaves are deciduous and
sensitive to frost; they die down and turn brown during the
winter.
Cultivation: The preference
is light shade to full sun, moist to dry conditions, and an acidic rocky or
sandy soil (especially the latter). This fern can spread aggressively. The
foliage is susceptible to various fungal diseases.
Range & Habitat: Bracken Fern is occasional to
locally common in northern and west-central Illinois, becoming less common
elsewhere in the state. This fern is widely distributed throughout the
world. Habitats include open
woodlands, sandy woodlands, rocky wooded slopes, sandstone cliffs, sandy
savannas, sandy thickets, sedge meadows, moist sand prairies, and sandy banks
of roadsides. Bracken Fern is particularly common in burned-over areas; its
dried leaves provide abundant fodder for wildfires.
Faunal Associations: Some insects are known to feed
on Bracken Fern. They include the caterpillars of some moths: Papaipema
pterisii (Bracken Borer Moth), Callopistria cordata (Silver-Spotted
Fern Moth), Callopistria granitosa (Granitosa Fern Moth), and
Homochlodes fritillaria (Pale Homochlodes). Extra-floral nectaries are
located at the bases of the major branches of each compound leaf. These
nectaries attract ants and other insects; their purpose is not well-understood.
The leaves are rarely eaten by mammalian herbivores because of their bitter
taste and toxicity. Young leaves produce a cyanide compound when they are
damaged. The leaves also contain an enzyme that can cause thiamin deficiency
and several carcinogenic compounds that are associated with cancer of the
digestive tract and bladder. Both cattle and horses have been seriously
poisoned by eating too much Bracken Fern. Because this fern often forms large
colonies, it provides leafy cover to many kinds of wildlife. The Indigo Bunting
and Chestnut-Sided Warbler have been known to construct nests on Bracken
Fern.
Photographic Location: Along a
path in a sandy savanna at the Iroquois County Conservation Area in Iroquois
County, Illinois.
Comments: This
large fern varies in attractiveness depending on the condition of its leaves.
Because of its relatively large size and tendency to be locally abundant,
Bracken Fern lends an exotic tropical aura to the temperate woodlands and
savannas where it occurs. This effect is magnified when it occurs with other
large ferns, like Osmunda regalis (Royal Fern) and Matteuccia
struthiopteris (Ostrich Fern). Because of the triangular shape of its 3
leafy branches and its tall erect petiole, Bracken Fern is easy to recognize,
although somewhat variable across its range: several varieties have been
described. In Illinois, var. latiusculum is by far the most common
variety of Bracken Fern; the only other variety in the state, var.
pseudocaudatum, is found in widely scattered locations in the southern half
of the state. This latter variety has terminal lobes that are even longer than
those of var. latiusculum: they are 6-15 times longer than they are
across.