About Pteridium aquilinum subsp. centrali-africanum Hieron.
This is a description of Pteridium aquilinum, common bracken, a herbaceous deciduous perennial that dies back to ground level each autumn. It produces large, roughly triangular fronds individually from an underground rhizome. Fronds grow to 0.3–1 metre (1–3+1⁄2 feet) tall, with the main stipe reaching up to 1 centimetre (1⁄2 inch) in diameter at the base. The rhizome itself can grow up to 3.5 metres (11+1⁄2 ft) deep, about 5 cm (2 in) in diameter, and up to 15 m (50 ft) long. Because new growth sprouts from this shared underground rhizome, common bracken typically forms dense colonies of genetically identical fronds. These colonies can be up to 650 years old, with individual rhizomes living up to 72 years. One studied colony 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 spring growth, the rhizome sends up coiled fiddleheads: vertical stalks covered in silver-grey hairs that can reach a metre or more in height before unfurling into full fronds. The density and area covered by a single rhizome maximizes its chance of biological success when producing new growth. Common bracken is native to Europe, Eastern Asia and North America, and now has an almost cosmopolitan distribution. In the Americas, it grows throughout the continental United States, the Canadian provinces of Ontario, Quebec, and Newfoundland, reaches as far north as southern Alaska, and extends south to northern Mexico and the Greater Antilles in the Caribbean. It grows as a weed in acidic upland pastures of northwestern Europe, and inhabits pastures, deciduous and coniferous woodlands, and hillsides, with a preference for acidic soils. It is an adaptable plant that readily colonises disturbed areas, and can grow aggressively even within its native range; for example, it has invaded heather (Calluna vulgaris (L.) Hull) stands on the North Yorkshire moors in England. In Ireland, it is found in open woodland and sandy pastures. Reproduction occurs via spores produced in sori of sporangia on the underside of fronds. The sori form narrow brown bands, and spores develop over July, August and September. Common bracken contains ptaquiloside, a carcinogenic compound. Ptaquiloside causes haemorrhagic diseases in ruminants, and tumours and haematological problems in non-ruminants. It is also correlated with oesophageal and gastric cancer in humans. Chronic consumption of bracken is linked to upper digestive tract (UDT) squamous cell carcinomas in cattle, with the most aggressive and serious tumours located in the caudal (lower) UDT. Areas with high stomach cancer rates, such as Japan and North Wales where young bracken stems are eaten as a vegetable, have not yet confirmed whether bracken consumption 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, and consumption of contaminated water or 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 is why rat studies of the toxin use storage at −20 °C (−4 °F). The carcinogen denatures almost completely at boiling temperature, and salt and baking soda also help volatilize the compound. 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 across many parts of the world, leading to varied cultural attitudes toward eating the plant. In the United Kingdom, where P. aquilinum grows prolifically, its rhizome was consumed during and after World War I, but the Royal Horticultural Society now explicitly advises against consumption due to toxicity. Bracken is a widely eaten wild vegetable in Korea, Japan, the Russian Far East, and parts of China, where it has historically been one of the most important wild food plants. When people from these cultures immigrate to new areas, they can usually access local bracken for traditional use due to the species' global ubiquity. In Korea, bracken is called gosari: it is soaked, parboiled, stir-fried, and commonly served as a side dish called namul, and it is a classic ingredient of bibimbap. In Japan, bracken is called warabi, 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, and can be preserved in salt, sake, or miso. Bracken shoots have been used to produce beer in Siberia, and by indigenous peoples of North America. Its rhizome can be ground into flour for bread, and historically was used to make a porridge called gofio in the Canary Islands. 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 Nooksack people and other Pacific Northwest tribes extensively ate the species' rhizome. Young bracken fronds are easy to harvest 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 consumption should be avoided by people without adequate preparation skills. In Finnish traditional medicine, bracken has been used in multiple remedies: Elias Lönnrot recommended 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. The leaves were used as filling in mattresses, as it was believed this would lessen rheumatic pain and drive away vermin.
