Northern Ontario Plant Database

General: A large perennial fern, usually 0.6—1 m tall in our area, with triangular 3-parted fronds that originate from creeping rhizomes, 0.3—1.5 m long; often forming extensive colonies. In ferns, the blade of the frond may be subdivided two times (bipinnate) or three times (tripinnate). In tripinnate fronds, the first divisions are called pinnae (singular: pinna), while the smallest divisions are called pinnules. Portions of pinnae and pinnules may be pinnately lobed (pinnatifid) rather than divided. Warning: When young fern fronds emerge in the spring, the developing frond (crozier) is coiled at the tip like the head of a violin. Unlike the young fronds of ostrich fern, which are edible, bracken fern croziers should not be eaten as they contain carcinogenic compounds.

Taxonomy: Pteridium aquilinum var. latiusculum (Desv.) Underw. ex A.Heller is the variety found across Ontario.

Stems: Underground rhizomes are horizontal and creeping.

Fronds: Herbaceous, with fronds dying back to the ground each winter; the stiff stalk of each frond (stipe) is 1.5—10 dm tall, smooth (glabrous), and grooved along the front. Front blades are narrowly to broadly triangular, about 20—80 cm long by wide, and separated into 3 tripinnate sections. The upper frond surface and midribs (rachis and costa) of each section and pinna are slightly hairy. Pinnae, arranged in opposite pairs along the rachis, are lanceolate and taper gradually to a narrow apex. Basal pinnules of each pinna are distinct, while upper portions of the pinna are pinnatifid. Pinnules are lanceolate to oblong, about 5—8 mm wide, and are attached to the costa at an angle between 45° and 60° degrees. Within each pinna, pinnules are alternately arranged and have dichotomous venation, with ultimate veins dividing into equal branches; pinnule margins are finely hairy and turned under (revolute). Fronds growing in the shade tend to have wider, horizontal blades, while fronds in open sunny sites have narrower, more erect blades. Fronds turn brown in autumn.

Reproductive structures/fertile fronds: Bracken ferns are monomorphic, with similar fertile and sterile fronds. Sporangia develop along the edges of the lower frond surface (in marginal sori); margins of the fertile pinnules fold over the sporangia, forming a false indusium along the margin. Fertile colonies are usually found on disturbed sites and occur less commonly in the north than in southern portions of their range.

Habitat and Range: Clearings, roadsides, old burns, forest edges, and open woodlands; usually on dry, acidic, sandy, or sterile soils. The eastern variety of bracken fern (var. latiusculum) has a Canadian range that extends from Newfoundland and southern Quebec west to southeastern Manitoba; a few disjunct locations are reported from British Columbia and southern Alberta.

Similar Species: Some species of woodfern (Dryopteris) have tripinnate fronds, but woodferns grow in tufts and bear dot-like sori on the lower surface of their fronds. Each sorus is covered with a broad horseshoe-shaped (reniform) indusium.