Pteridium aquilinum (bracken, brake, or common bracken), also known as eagle fern, is a species of fern occurring in temperate and subtropical regions in both hemispheres. The extreme lightness of its spores has led to its global distribution.

Common bracken was first described as Pteris aquilina by Carl Linnaeus, in Volume 2 of his Species Plantarum in 1753. The origin of the specific epithet derived from the Latin aquila "eagle". In the reprint of the Flora Suecica in 1755, Linnaeus explains that the name refers to the image of an eagle seen in the transverse section of the root. In spite of this, the opinion has been forwarded that the name pertains to the shape of the mature fronds appearing akin to an eagle's wing. However, medieval scholars, including Erasmus, thought the pattern of the fibers seen in a transverse section of the stipe resembled a double-headed eagle or oak tree.

Common bracken is a herbaceous perennial plant, deciduous in winter. The large, roughly triangular fronds are produced singly, arising upwards from an underground rhizome, and grow to 0.3–1 m (1–3ft) tall; the main stem, or stipe, is up to 1 cm (0.4 in) diameter at the base. It dies back to ground level in autumn.

The fiddleheads/crosiers of Pteridium aquilinum have been known to be eaten, but they contain carcinogens, so this practice is not prevalent.

Sporangia are formed in sori on the underside of the frond. They are arranged in narrow brown bands, and form spores over July, August, and September.

Bracken grows in pastures, deciduous and coniferous woodlands, and hillsides. It prefers acidic soils.

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