bracken (Pteridium aquilinum), also called brake, a member of the fern family Dennstaedtiaceae (plant division Pteridophyta), widely distributed throughout the world in temperate and tropical regions. Pteridium aquilinum is usually separated into 12 varieties or subspecies. Some botanists classify most or all of these varieties as separate species, a topic that is controversial among taxonomists. P. aquilinum is perhaps the most broadly distributed of all fern species and among the most wide-ranging of all vascular plants. Five of the varieties occur in North America and Great Britain. Variety pubescens grows from Alaska to Mexico, east to Wyoming, Colorado, and Texas. Variety latiusculum, growing also in northern Europe and eastern Asia, occurs from Newfoundland to Minnesota, south to Oklahoma and Tennessee. Variety pseudocaudatum grows from Massachusetts to Florida, west to Missouri and Texas. Variety caudatum, a West Indian plant, grows in southern Florida. Variety aquilinum is common in Great Britain.
This species has a perennial black rootstock that creeps extensively underground and at intervals sends up fronds. Individual rhizomes have been documented as spreading up to about 400 metres (1,300 feet) in length, making bracken one of the largest plants in the world. The fronds may reach a height of 5 metres (16 feet) or more and, despite dying in autumn, often remain standing throughout the winter, affording cover for game in some regions. The fronds are used as thatching for houses and as fodder and are cooked as vegetables or in soups in some parts of Asia. However, this can be quite dangerous, as the leaves of bracken contain an array of poisonous and carcinogenic compounds.
Bracken is an aggressive colonizer of open ground and readily invades pastures and fields. Once established, the deep-set rhizomes are nearly impossible to eradicate. Because of its ability to render land unfit for livestock and its tendency to shade out other plant species (including some of conservation concern), bracken is considered to be among the world’s worst weeds.