Pteridium aquilinum

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 the father of taxonomy, Carl Linnaeus, in Volume 2 of his Species Plantarum in 1753. The origin of the specific epithet derived from the Latin aquila “eagle”, but what it pertains to has been a matter of some debate. It is generally held to be the shape of the mature fronds appearing akin to an eagle’s wing. However, medieval scholars, including Erasmus, thought the pattern of the fibres seen in a transverse section of the stipe resembled a double-headed eagle or oak tree. It was given its current binomial name by Friedrich Adalbert Maximilian Kuhn in 1879. It was traditionally treated as the sole species in the genus Pteridium (brackens); authorities have split and recognised up to 11 species in the genus, however. It 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 1–3 m (3–10 ft) tall; the main stem, or stipe, is up to 1 cm (0.4 in) diameter at the base. An adaptable plant, it readily colonises disturbed areas. It can even be invasive in countries where it is native, such as England, where it has invaded heather (Calluna vulgaris (L.) Hull) stands on the North Yorkshire moors. The plant contains the carcinogenic compound ptaquiloside, and communities (mainly in Japan) where the young stems are used as a vegetable have some of the highest stomach cancer rates in the world. Consumption of ptaquiloside-contaminated milk is thought to contribute to human gastric cancer in the Andean states of Venezuela. The spores have also been implicated as carcinogens. It has been suggested that selenium supplementation can prevent as well as reverse the immunotoxic effects induced by ptaquiloside from Pteridium aquilinum.