About Pteridium aquilinum (L.) Kuhn
Pteridium aquilinum, commonly called common bracken, is a deciduous herbaceous perennial plant. It produces large, roughly triangular fronds that grow singly upward from an underground rhizome, reaching 0.3–1 metre (1–3+1⁄2 feet) in height. The main stem (stipe) grows up to 1 centimetre (1⁄2 inch) in diameter at its base, and the entire above-ground plant dies back to ground level each autumn. The underground rhizome can reach up to 3.5 metres (11+1⁄2 ft) deep, around 5 cm (2 in) in diameter, and up to 15 m (50 ft) long. Because the plant regrows from this underground rhizome each spring, P. aquilinum typically forms dense colonies of genetically identical fronds. These colonies can be as much as 650 years old, with individual rhizomes living up to 72 years. One colony studied by Eino Oinonen in Raakkyla, North Karelia, Finland measured 489 m (1,604 ft) in diameter, and was estimated to be over 1400 years old based on its growth rate. At the start of the spring growing cycle, the rhizome sends up fiddleheads first. A single rhizome covers a large area with high density, which maximizes its biological success when producing new growth. New growth appears as vertical, coiled stalks covered in silver-grey hairs; these stalks can reach a metre or more in height before unfurling into mature fronds.
Common bracken is native to Europe, Eastern Asia, and North America, and now has an almost cosmopolitan distribution. In the Americas, it occurs across the continental United States, and in the Canadian provinces of Ontario, Quebec, and Newfoundland. Its range extends north to southern Alaska, and south to northern Mexico, as well as the Greater Antilles in the Caribbean. It is considered a weed in acidic upland pastures of northwestern Europe. Bracken grows in pastures, deciduous woodlands, coniferous woodlands, and hillsides, and prefers acidic soils. It is an adaptable plant that readily colonizes disturbed areas, and can be aggressive even within its native range; for example, in England, it has invaded stands of heather (Calluna vulgaris (L.) Hull) on the North Yorkshire moors. In Ireland, it is found in open woodland and sandy pastures.
For reproduction, sporangia form in sori on the underside of fronds, arranged in narrow brown bands, and produce spores from July through September.
This plant contains ptaquiloside, a carcinogenic compound. Ptaquiloside is known to cause haemorrhagic diseases in ruminants, and tumours plus haematological problems in non-ruminants. It is also correlated with oesophageal and gastric cancer in humans. Chronic consumption of bracken is associated with upper digestive tract (UDT) squamous cell carcinomas in cattle (ruminants), with the most aggressive and serious tumours located in the caudal (lower) UDT. High rates of stomach cancer occur in Japan and North Wales, where young bracken stems are eaten as a vegetable, but it remains unknown whether bracken contributes to these cancers or if another cause is responsible. Consumption of milk contaminated with ptaquiloside is thought to contribute to human gastric cancer in the Andean states of Venezuela. Bracken spores have also been implicated as carcinogens, and consumption of contaminated water and meat may also be dangerous. However, ptaquiloside is water-soluble, and its levels are reduced by soaking bracken in cool water. Korean and Japanese cooks have traditionally soaked bracken shoots in water and ash to detoxify the plant before eating. Ptaquiloside also degenerates at room temperature, which explains why rat studies of the toxin used material stored at −20 °C (−4 °F). At boiling temperature, the carcinogen denatures almost completely. Salt and baking soda also help volatilize the chemical. Selenium supplementation has been suggested to both prevent and reverse the immunotoxic effects induced by ptaquiloside from Pteridium aquilinum.
Despite its confirmed toxicity, P. aquilinum is the fifth most widely distributed common weed species globally, and has a long history of human consumption in many parts of the world. Its toxicity and wide distribution have led to varying cultural attitudes toward consumption. In the United Kingdom, where P. aquilinum grows prolifically, the rhizome was eaten during and after World War I, but the Royal Horticultural Society now explicitly advises against consumption due to toxicity. Bracken is a widely eaten vegetable in Korea, Japan, the Russian Far East, and parts of China, where it has historically been one of the most important collected wild vegetables. When people from these countries immigrate to new areas, P. aquilinum's global ubiquity allows them to continue accessing bracken for consumption. In Korea, bracken is called gosari; it is soaked, parboiled, stir-fried, and often served as a side dish (namul), and is a classic ingredient of bibimbap. In Japan, bracken is known as warabi (蕨, ワラビ), and a jelly-like starch made from it is a key ingredient in the chilled dessert warabimochi. As a type of sansai (mountain vegetable), young bracken shoots are steamed, boiled, or cooked in soups. Shoots are also preserved in salt, sake, or miso. Bracken shoots have been used to produce beer in Siberia, and by indigenous peoples of North America. The rhizome can be ground into flour to make bread. In the Canary Islands, the rhizome was historically used to make a porridge called gofio. In the Mediterranean region, bracken leaves are used to filter sheep's milk and store freshly made ricotta cheese. The name Nooksack means "always bracken fern place" in the Nooksack language, and the rhizome was eaten extensively by the Nooksack people and other tribes of the Pacific Northwest. Young bracken fronds can be harvested easily, and should be cooked for 30 to 60 minutes before consumption. Mature bracken is toxic due to thiaminase, which can be destroyed by cooking. Consumption should be avoided if you do not have sufficient preparation skill.
In Finnish traditional medicine, bracken has been used in a variety of remedies. Elias Lönnrot advised using a powder made from the plant's roots to drive away maggots. A decoction of bracken was used to treat stomach problems, gout, and joint pain. Leaves were used as filling for mattresses, as they were believed to reduce rheumatic pain and drive away vermin.
