| Bracken | |
|---|---|
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Pteridophyta |
| Class: | Pteridopsida |
| Order: | Dennstaedtiales |
| Family: | Dennstaedtiaceae |
| Genus: | Pteridium |
| Species | |
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Pteridium aquilinum |
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Bracken are several species of large, coarse ferns of the genus Pteridium. Ferns (Pteridophyta) are vascular plants that have alternating generations, large plants that produce spores and small plants that produce sex cells (eggs and sperm). Brackens are in the family Dennstaedtiaceae, which are noted for their large, highly divided leaves. They are commonly found on moorland. Brackens are cosmopolitan, being found on all continents except Antarctica and in all environments except deserts. The genus probably has the widest distribution of any fern genus in the world.
In the past, the genus was commonly treated as having only one species, Pteridium aquilinum, but the recent trend is to subdivide it into about ten species.
As ferns, brackens do not have seeds or fruits, but the immature fronds, known as fiddleheads, are edible.
The word bracken is of Old Norse origin, related to the Swedish word bräken, meaning fern.
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Evolutionarily, bracken may be considered to be one of the most successful ferns. It is also one of the oldest, with fossil records of over 55 million years old having been found. The plant sends up large, triangular fronds from a wide-creeping underground rootstock, and may form dense thickets. This rootstock may travel a metre or more underground between fronds. The fronds may grow up to 2.5 m (8 ft) long or longer with support, but typically are in the range of 0.6–2 m (2–6 feet) high. In cold environments bracken is winter-deciduous, and, as it requires well-drained soil, is generally found growing on the sides of hills.
It is an herbaceous perennial plant, deciduous in winter. The fronds are produced singly from an underground rhizome, and grow to be 1–3 m tall; the main stem is up to 1 cm diameter at the base. The rhizomes typically grow to a depth of 50 cm, although in some soils this may extend to more than a metre.
The spores used in reproduction are produced on the underside of the leaf in structures found on the edges of the leaf called sori. The linear pattern of these is different from other ferns which are circular and towards the centre.
Pteridium aquilinum (Bracken or Common Bracken) is the most common species with a cosmopolitan distribution, occurring in temperate and subtropical regions throughout much of the world, including most of Europe, Asia, and North America in the Northern Hemisphere, and Australia, New Zealand and northern South America in the Southern Hemisphere. It is a prolific and abundant plant in the highlands of Great Britain. It is limited to altitudes of below 600 metres in the UK, does not like extreme cold temperatures, poorly drained Marshes or Fen. It causes such a problem of invading pastureland that at one time the British government had an eradication programme. Special filters have even been used on some British water supplies to filter out the bracken spores.[1] NBN distribution map for the United Kingdom
It has been observered growing in soils from pH 2.8 to 8.6. Exposure to cold or high pH inhibits its growth.
Woodland fungi can be found growing under the bracken canopy, for example Mycena epipterygia. Both Camarographium stephensii and Typhula quisquiliaris grow primarily from dead bracken stems.
Allelopathy: Bracken fern is known to produce and release allelopathic chemicals, which is an important factor in its ability to dominate other vegetation, particularly in regrowth after fire. Herb and tree seedling growth may be inhibited even after bracken fern is removed, apparently because active plant toxins remain in the soil.
Brackens substitute the characteristics of a woodland canopy, and are important for giving shade to European plants such as common bluebell and wood anemone, where the woodland does not exist. These plants are intolerant to stock trampling. Dead bracken provides a warm microclimate for development of the immature stages. Climbing corydalis, wild gladiolus and chickweed wintergreen also seem to benefit from the conditions found under bracken stands.
The high humidity helps mosses survive underneath including Campylopus flexuosus, Hypnum cupressiforme, Polytrichum commune, Pseudoscelopodium purum and Rhytidiadelphus squarrosus.
Brackens of the northern hemisphere are used as food plants by the larvae of some Lepidoptera species including Dark Green Fritillary, Dot Moth, High Brown Fritillary, Gold Swift, Map-winged Swift, Pearl-bordered Fritillary, Orange Swift, Small Angle Shades, Small Pearl-bordered Fritillary. They also form an important ecological partnership with plants such as violet and cow-wheat (Melampyrum pratense) for various Boloria Fritillary species.
It is also a favoured haunt of the sheep tick Ixodes ricinus which can carry Lyme Disease.
Between 27 to 40 invertebrates (including nine moths) in the UK feed on bracken. These include the sawfly, a planthopper (Dytroptis pteridis), the map-winged swift moth caterpillar, brown silver-line moth caterpillar (Petrophora chlorosata) and Paltodora cytisella. The numbers feeding on the bracken increase as the season progresses due to the decreasing levels of toxin, and the production of nectaries in the spring, food for ants which in turn may kill any herbivorous insects in the vicinity.
Some birds such as the whinchat and the nightjar use bracken as their preferred habitats. The nightjar may lay its eggs on the bare ground under the bracken. The skylark often nests in bracken and uses it for cover. Other birds known to nest in or beneath bracken include the willow warbler (it will also use bracken to construct its nest), the tree pipit, the yellowhammer, the ring ouzel, the woodcock and the twite.
The European adder can be found basking on bracken, the colour of their skin concealing them.
Bracken fiddleheads (the immature, tightly curled emerging fronds) have been considered edible by many cultures throughout history, and are still commonly used today as a foodstuff. Bracken fiddleheads are either consumed fresh (and cooked) or preserved by salting, pickling, or sun drying. In Korea[2], where they are called gosari (고사리), they are a typical ingredient in the mixed rice dish called bibimbap.
The Royal Horticultural Society recommends against consumption of bracken either by humans or livestock, since it contains carcinogens linked with oesophageal and stomach cancer. [3]
Both fronds and rhizomes have been used to brew beer, and the rhizome starch has been used as a substitute for arrowroot. Bread can be made out of dried and powered rhizomes alone or with other flour. American Indians cooked the rhizomes, then peeled and ate them or pounded the starchy fiber into flour. In Japan, starch from the rhizomes is used to make confections.
Bracken is called wiwnunmí útpas ‘huckleberry’s blanket’ by the Umatilla Indians of the Columbia River in the United States Northwest. The fronds were used to cover a basket full of huckleberries in order to keep them fresh.
The Māori of New Zealand used the rhizomes of P. esculentum (aruhe) as a staple food, especially for exploring or hunting groups away from permanent settlements; much of the widespread distribution of this species in present-day New Zealand is in fact a consequence of prehistoric deforestation and subsequent tending of aruhe stands on rich soils (which produced the best rhizomes). The rhizomes were air-dried so that they could be stored and became lighter; for consumption, they were briefly heated and then softened with a patu aruhe (rhizome pounder); the starch could then be sucked from the fibers by each diner, or collected if it were to be prepared for a larger feast. Patu aruhe were significant items and several distinct styles were developed.[4]
In East Asia, Pteridium aquilinum (fernbrake or bracken fiddleheads) is eaten as a vegetable, called warabi (蕨 / わらび) in Japan, gosari (고사리) in Korea, and juécài (蕨菜) in China and Taiwan. In Korea, a typical banchan (small side dish) is gosari-namul (고사리나물) that consists of prepared fernbrake that has been sauteed. It is a component of the popular dish bibimbap.
Bracken has been shown to be carcinogenic in some animals[5] and some have suggested it could have some part in causing the high incidence of stomach cancer in Japan.[5] It is currently under investigation as a possible source of new insecticides.[6]
Uncooked bracken contains the enzyme thiaminase, which breaks down thiamine. Eating excessive quantities of bracken can cause beriberi, especially in creatures with simple stomachs. Ruminants are less vulnerable because they synthesize thiamine.
It was traditionally used (and still is in certain areas like mid Wales) for animal bedding, which later broke down to a rich mulch which could be used as fertilizer.[7]
When used by gardeners as a winter mulch it has been shown to reduce the loss of potassium and nitrogen and to lower soil pH.[7]
Other uses were as packing material for products such as earthenware, as a fuel, as a form of thatch. The ash was used for degreasing woolen cloth.
The ash of bracken fern was used in making forest glass in Central Europe from about 1000 to 1700.
Bracken is currently harvested in the Lake District, Cumbria, United Kingdom to make commercial composts.
The plant is carcinogenic to animals such as mice, rats, horses and cattle when ingested, although they will usually avoid it unless nothing else is available. Young stems are quite commonly used as a vegetable in China, Japan and Korea. However, some researchers suspect a link between consumption and higher stomach cancer rates.[5] The spores have also been implicated as a carcinogen. Danish scientist Lars Holm Rasmussen released a study in 2004 showing that the carcinogenic compound in bracken, ptaquiloside or PTQ, can leach from the plant into the water supply, which may explain an increase in the incidence of gastric and oesophageal cancers in bracken-rich areas.[8]
In cattle, bracken poisoning can occur in both an acute and chronic form, acute poisoning being the most common. In pigs and horses bracken poisoning induces vitamin B deficiency.[9] Poisoning usually occurs when there is a shortage of available grasses such as in drought or snowfalls.
It damages blood cells and destroys thiamine (vitamin B1). This in turn causes beriberi, a disease linked to nutritional deficiency.
Also it contains ptaquiloside, pterosins and some metabolites [1]
Various techniques are recommended by Natural England to control bracken either individually or in combination:
Selective sprays like Starane , Access, Metsulfuron 600WG etc. work well but only if sprayed in late autumn so the rhizomes store food for winter and hence absorb the poison.