Bracken Fern
Pteridium aquilinum latiusculum
Hay-Scented Fern family (Dennstaedtiaceae)

Description: This perennial fern develops an erect and rather stout petiole up to 3' tall, from which there extends a single compound leaf up to 3' long and 3' across that is triangular in outline. 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; its upper surface is glabrous or nearly so, while its lower surface is glabrous to sparsely short-pubescent. The compound leaf has an irregular structure; it is mostly bipinnate-pinnatifid and, to a lesser extent, tripinnate-pinnatifid. Along the central rachis of the fern, there are up to 12 pairs of leaflets that become progressively smaller in size; the leaflets toward the base of the rachis are much longer than the leaflets toward its tip. Individual leaflets are mostly pinnate-pinnatifid, although some of the larger leaflets toward the base of the rachis are partly bipinnate-pinnatifid; there are up to 15 pairs of subleaflets per leaflet that gradually become shorter toward its tip, where there is a terminal subleaflet.  The subleaflets are mostly pinnatifid; they have up to 12 pairs of oblong lobes and a terminal lobe. When ultimate leaflets are present, they are either smooth or they have up to 4 pairs of basal lobes that are oblong in shape. The terminal lobes of leaflets and 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 they are wide. The petiole, central rachis, and lateral stalks of each compound leaf are light green to yellowish green and glabrous to finely short-pubescent.

The margins of the subleaflets, ultimate leaflets, and lobes are smooth and sometimes slightly undulate; they curve 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 the summer or autumn. The root system system is fibrous and long-rhizomatous; individuals rhizomes can extend many yards (or meters), sending up new clonal shoots every 1-6 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: The native Bracken Fern is occasional to locally common in northern and west-central Illinois, becoming less common elsewhere in the state (see Distribution Map). This fern is widely distributed throughout the world. Habitats include open woodlands, sandy woodlands, rocky wooded slopes, sandstone cliffs, sandy savannas, sandy thickets, stabilized foredunes near Lake Michigan, 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). Other insects that feed on this fern include larvae of the sawfly Aneugmenus flavipes, larvae of the sawfly Strongylogaster multicincta, the aphid Macrosiphum ptericolens, and the aphid Mastopoda pteridis. 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 thiamine 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: A stabilized foredune at the Indiana Dunes State Park in NW Indiana, a sandy woodland at the Oak Openings Nature Preserve in NW Ohio, and 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 compound leaves 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.