About Pteridium aquilinum subsp. pinetorum (C.N.Page & R.R.Mill) J.A.Thomson
Pteridium aquilinum subsp. pinetorum, commonly called common bracken, is a deciduous herbaceous perennial plant. Its large, roughly triangular fronds grow individually 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 the base, and the entire plant dies back to ground level each autumn. The rhizome itself can grow 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 bracken regrows each spring from this shared underground rhizome, it typically forms dense colonies of genetically identical fronds. These colonies can be as much as 650 years old, and individual rhizomes can live 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, fiddleheads first emerge from the rhizome. The density and area covered by a single rhizome maximizes its chance of biological success when producing new growth. New growth appears as vertical, coiled stalks covered in silver-grey hairs, which can reach a metre or more in height before unfurling into mature fronds. 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 and the Greater Antilles in the Caribbean. It grows as a weed in acidic upland pastures of northwestern Europe. Bracken grows in pastures, deciduous and coniferous woodlands, and hillsides, and prefers acidic soils. It is an adaptable plant that readily colonises disturbed areas, and can be aggressive even within its native range; for example, in England, it has invaded heather (Calluna vulgaris (L.) Hull) stands on the North Yorkshire moors. In Ireland, bracken is found in open woodland and sandy pastures. Bracken reproduces via sporangia that form in sori on the underside of the frond. These sori are arranged in narrow brown bands, and produce spores from July through September. The plant contains the carcinogenic compound ptaquiloside. Ptaquiloside is known to cause haemorrhagic diseases in ruminants, and tumours and haematological problems in non-ruminants, and it is correlated with oesophageal and gastric cancer in humans. Chronic consumption of bracken is also associated with squamous cell carcinomas of the upper digestive tract (UDT) in cattle, 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 is not confirmed whether bracken contributes to these cancers or if they can be attributed to other causes. Consumption of ptaquiloside-contaminated milk is thought to contribute to human gastric cancer in the Andean states of Venezuela. Bracken spores have also been implicated as carcinogens. Consumption of contaminated water and meat from animals that ate bracken may also be dangerous. However, ptaquiloside is water-soluble, and its concentration is 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 on the toxin used toxin 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's status as the fifth most widely distributed common weed species in the world means it has a long history of human consumption across many regions. 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 consumed during and after World War I. However, the Royal Horticultural Society now explicitly advises against consuming bracken due to its 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 wild vegetables consumed. After immigrating to new locations, populations from these countries have been able to access bracken due to the plant's global ubiquity. In Korea, bracken is called gosari. It is soaked, parboiled, stir-fried, and often served as a side dish called namul. It is also a classic ingredient of bibimbap. In Japan, bracken is called 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 can also be preserved in salt, sake, or miso. Bracken shoots have been used to produce beer in Siberia, and among 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. In the Nooksack language, the name Nooksack translates to "always bracken fern place", 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 eating. Mature bracken is toxic due to the enzyme thiaminase, which can be destroyed by cooking. Bracken should be avoided if you do not have sufficient preparation skill. In Finnish traditional medicine, bracken has been used as a remedy in multiple ways: 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 in mattresses, as it was believed to reduce rheumatic pain and drive away vermin.
