Common Name: Bracken fern, Brake fern, Brake, Eagle fern, Female fern, Fiddlehead, Hog brake, Pasture brake, Western Brackenfern – The word bracken is considered by etymologists to be of Scandinavian provenance (Old Swedish brækne). The initial meaning is believed to have referred to brushwood, as broken trees were referred to as “brakes,” at one time the past tense of break. The second common name “Brake fern” is evidence of this association. It is likely that this nomenclature arose from the habitat of the Bracken fern, in “broken” wooded areas.
Scientific Name: Pteridium aquilinum – The generic name is from the Greek word pteris, which means fern. The species name is from aquila, the Latin word for eagle; aquilinum means relating to an eagle. The tripartite shape of the blade is suggestive of an eagle in flight. It is known by a number of other scientific names, including Asplenium aquilinum, Allosorus aquilinus, Ornithopteris (Bird fern) aquilina, Felix aquilina and Pteris latiscula.
Potpourri: The Bracken or Brake fern is likely the most prolifically global of the plants that make up the phylum or division Pteridophyta that we commonly know as ferns. It is found on every continent except Antarctica and in every environment excepting those desiccated by an inadequacy of rainfall. Although the species is sometimes subdivided into about 12 varieties, it is generally considered to be singular, and as such may well be the most ubiquitous of all land vascular plants, weeds notwithstanding. It has several names in many languages that include grande fougère and fougère d’aigle in France, warabi in Japan and gosari namul in Korea, a reflection of its ubiquity and its distinctive characteristics.
The proliferation of the Bracken or Brake fern has earned it the sobriquet “the weed fern.” It predominates over other plants in some habitats to the extent that it forms dense, almost impenetrable coppices for which it is considered a nuisance in some areas, notably the British Isles. It was once considered to encroach on pastureland to the extent that the British government initiated an eradication program. It is estimated that its encroachment rate into new areas is between 1 and 3 percent per annum. In some areas, it is so prolific that special filters must be used on water sources to remove the spores. In Far From the Madding Crowd, Thomas Hardy writes “what appeared like an impassable thicket was in reality a brake of fern now withering fast,” the heroine Bathsheba ironically choosing this for her hidden forest bower.
The Bracken fern’s prodigality is in part due to its successful use of the rhizome structure in extending its range; a rhizome is essentially a stem that grows horizontally underground with upward extensions that form aerial shoots along the upper surface and roots along the lower surface. The main rhizome of the bracken fern can be several centimeters in diameter and can extend rapidly to expand the network of the plant over a broad area; leaf-bearing lateral branches produce the characteristic fronds along the length of the rhizome. The fronds are thrice-divided; the pinnae are divided into pinnules, the blade extending as much as a meter above the ground. The spores are on the underside of the margins of the fertile frond. The bracken fern is readily identifiable; its most notable characteristics are the fused pinnae structures at the tips of the blades and the leathery and coarse-textured leaves.
A second reason for the dominance of the bracken fern over its competitors is its allelopathy; it produces chemical compounds that inhibit the growth of other plants. Allelopathy (from the Greek allel meaning “of one another” and pathos meaning disease) is a survival adaptation of a number of plants, including black walnut, sugar maple, sycamore, and black cherry. Among the known chemical compounds are sesquiterpenes, which are naturally occurring alcohols, phytosterols, similar to cholesterol and closely related to the hormone in insects that promotes molting, thiaminase which inhibits the uptake of thiamin (vitamin B1), ptaquiloside, a lactone toxin that affects the bone marrow and is probably carcinogenic, and cyanogenic glycosides that yield hydrogen cyanide. The chemical complexity of the bracken fern is manifest in the many applications to which it has been historically exploited that range from foodstuff to medicinal and in the equally numerous problems with its toxicity.
The newly emerging fronds of the bracken fern have long been gathered in the spring and are generally consumed after drying, salting or pickling, though they are sometimes eaten fresh. The fern crosiers, known in the vernacular as fiddleheads, are a staple food product in Japan and Korea, where they are typically consumed in the mixed rice dish bibimbap. However, the bracken fern contains the compound ptaquiloside, which was found to be carcinogenic to laboratory animals in 1978 by the Japanese pathologist Iwao Hirono; it may not be coincidental that Japan and Korea have among the highest rates of stomach cancer when compared to the rest of the world. It is likely that food processing methods like heating eliminates the toxins, as the rhizomes of the bracken fern have historically been consumed as food or used in food processing. Dried and powdered rhizomes have been used in brewing beer and as a substitute for arrowroot, a tropical tuber used to make gluten-free flour. Native Americans purportedly cooked the rhizomes and either peeled and ate them whole or pounded them into a flour to make bread. This was reputed to have therapeutic effects in the treatment of bronchitis and as a deterrent against parasitic worms. Bracken rhizomes were a staple food of the natives of New Zealand, the Maori. They were dried to reduce the weight for use by deployed hunting parties; they developed a tool called patu aruhe (literally rhizome pounder) that was used to soften the tough stem so that the starch could be sucked out.
The toxicity of the bracken fern has always been a serious problem for grazing animals, exacerbated by the extensive growth of the fern in areas adjacent to pastures and fields. Monogastric animals like horses and swine are particularly susceptible, though all animals are affected. The major problem is the compound thiaminase, an enzyme which depletes thiamine and causes a serious vitamin deficiency that in humans is called beriberi, from the Sinhalese words for “I cannot, I cannot,” repeated for emphasis; the symptoms include weakness and loss of feeling in the feet and legs due to swelling of the lower half of the body. The Polish chemist Casimir Funk isolated the chemical in unpolished rice that had been found to eliminate the disease and determined that it was a “vital amine,” from which the word vitamin evolved. The lack of vitamin B1 results in degeneration of the myelin of the nerves that control muscle movement. The symptoms start with a condition known as “bracken staggers” as the muscles degenerate. Untreated, death can result in less that a fortnight; the antidote is daily injections of thiamine.
Ruminants such as cattle and sheep are also subject to poisoning from eating bracken, though not from thiamine deficiency, as the bacteria in the rumen destroys thiaminase. The other toxins in bracken, such as ptaquiloside, are responsible for a diminution of bone marrow activity that reduces the production of red and white blood cells and platelet production. Cattle grazing on bracken over several months will have an increased temperature, a reduction in weight and a susceptibility to bruising and bleeding. The resultant anemia can cause death within a week of the manifestation of the condition. The only remedy is to remove the cattle from the source of bracken and to provide supportive care to allow for the toxins to pass through the system and for normal blood production to resume. Transfusions, though possible, are not economically feasible.
Bracken has played a significant role in the culture of Western Civilization; it was used to pay the rent in the middle ages as a measure of its value. Bracken fronds are highly absorbent due to their high surface area and they additionally retain their fullness under the weight of compaction. Harvested bracken ferns were accordingly used as thatch for roofs, and, ironically given their overall toxicity, as livestock bedding. Bracken rhizomes are noted for their ability to extract phosphorous and potassium from the soil, accumulating stores of these minerals in their extensive branching networks. Potash extracted from bracken was used in soap making and in the manufacture of bleach through the mid 19th Century. Bracken is currently under evaluation for use as a natural fertilizer, taking advantage of its high levels of potash, and as a biofuel; it has long been used to make especially hot fires. Bracken ferns have a higher caloric output at than wood at 21 versus to 16 billion joules per ton.