Bracken
Bracken is a genus of large, cosmopolitan, coarse ferns in the family Dennstaedtiaceae. Ferns are vascular plants that undergo alternation of generations, having both large plants that produce spores and small plants that produce sex cells in its life cycle. Brackens are noted for their large, highly divided leaves. They are found on all continents except Antarctica, though their typical habitat is moorland. The genus probably has the widest distribution of any fern in the world.
The word bracken is of Old Norse origin, related to Swedish bräken and Danish bregne, both meaning fern. 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.
Like other ferns, brackens do not have seeds or fruit, but reproduce by spores. The immature fronds, known as fiddleheads, are sometimes eaten, although some are thought to be carcinogenic.
Description
Bracken is one of the oldest ferns, with fossil records from the Eocene period 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 long or longer with support, but typically are in the range of high. In cold environments, bracken is deciduous and, as it requires well-drained soil, is generally found growing on the sides of hills.Fern spores are contained in structures found on the underside of the leaf called sori. The sori of bracken are located in a line next to the leaf-edge and are distinctly different from that in most other ferns, where the sori are circular and occur towards the center of the leaf.
Species
Distribution and habitat
Pteridium aquilinum is the most common species with a cosmopolitan distribution, occurring in temperate and subtropical regions throughout much of the world. It is a prolific and abundant plant in the moorlands of Ireland, where it is limited to altitudes of below 600 metres. It does not like poorly drained marshes or fen. It has been observed growing in soils from pH 2.8 to 8.6. Exposure to cold or high pH inhibits its growth. It causes such a problem in invading pasturelands 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.Bracken is a characteristic moorland plant in Ireland which over the last decades has increasingly out-competed characteristic ground-cover plants such as moor grasses, cowberry, bilberry, and heathers, and now covers a considerable part of upland moorland.
Once valued and gathered for use in animal bedding, tanning, soap and glass making, and as a fertiliser, bracken is now seen as a pernicious, invasive, and opportunistic plant, taking over from the plants traditionally associated with open moorland and reducing easy access by humans. It is toxic to cattle, dogs, sheep, pigs, and horses, and is also linked to cancers in humans. It can harbour high levels of sheep ticks, which can pass on Lyme disease. Grazing provided some control by stock trampling, but this has almost ceased since the 2001 foot-and-mouth disease outbreak reduced commercial livestock production. Global climatic changes have also suited bracken well and contributed to its rapid increase in land coverage.
Bracken is a well-adapted pioneer plant which can colonise land quickly, with the potential to extend its area by as much as 1%–3% per year. This ability to expand rapidly at the expense of other plants and wildlife can cause major problems for land users and managers. It colonises ground with an open vegetation structure, but is slow to colonise healthy, well managed heather stands.
Bracken presents a threat to biodiversity. Many plant species occur only on upland moorland, tied to unique features in the habitat. The loss and degradation of such areas due to the dominance of bracken has caused many species to become rare and isolated.
The Bracken is known to form large fern prairies. Some of these are natural but others can be formed via fires created by Humans. Brackens are also key parts of other types of savannah such as Pine savannah and Pineyards.
Ecology
Evolutionarily, bracken may be considered one of the most successful ferns. It is considered highly invasive, and can survive in acid soils.Fungal associations
Woodland fungi such as Mycena epipterygia can be found growing under the bracken canopy. Both Camarographium stephensii and Typhula quisquiliaris grow primarily from dead bracken stems.Other plant associations
Bracken 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. Its chemical emissions, shady canopy, and thick litter inhibit other plant species from establishing themselves – with the occasional exception of plants which support rare butterflies. Herb and tree seedling growth may be inhibited even after bracken is removed, apparently because active plant toxins remain in the soil.Bracken substitutes the characteristics of a woodland canopy, and is 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 in the stands helps mosses survive underneath, including Campylopus flexuosus, Hypnum cupressiforme, Polytrichum commune, Pseudoscelopodium purum and Rhytidiadelphus squarrosus.
Uses
Food
Bracken fiddleheads have been eaten by many cultures throughout history, either fresh, cooked, or pickled. Pteridium aquilinum is especially common in East Asian cuisine.In Korea, bracken is known as gosari, and is a typical ingredient in bibimbap, a popular mixed rice dish. Stir-fried bracken is also a common side dish in Korea.
In Japan, bracken is known as warabi, and is steamed, boiled, or cooked in soups. Warabimochi bracken jelly, named after its resemblance to mochi rice cakes, is a popular traditional dessert, although commercial variants are often made with cheaper potato starch instead. The fiddleheads are also preserved in salt, sake, or miso.
In China, bracken is known as juecai, and is eaten like vegetables or preserved by drying. Also called "fernbrake", it is used as a vegetable in soups and stews.
Bracken rhizomes can be ground into flour to make bread. In the Canary Islands, the rhizome was historically used to make a porridge called gofio. Both fronds and rhizomes have been used to produce beer in Siberia, and among indigenous peoples of North America.
Bracken leaves are used in the Mediterranean region to filter sheep's milk, and to store freshly made ricotta cheese.
P. esculentum rhizomes were traditionally used by the Māori people of New Zealand as a staple food, and are known as aruhe. They were eaten by exploring or hunting groups away from permanent settlements. The plant was widely distributed across New Zealand as a result of prehistoric deforestation, and planting on rich soils, which produced the best rhizomes. The rhizomes were dried, and could be heated and softened with a pounder, after which the starch could be sucked from the fibers. Patu aruhe were important ritual items, and several distinct styles were developed.
Others
Bracken has traditionally been used for animal bedding, which later breaks down into a rich mulch that could be used as fertilizer. It is still used this way in Wales. It is also used as a winter mulch, which has been shown to reduce the loss of potassium and nitrogen in the soil, and to lower soil pH.Toxicity
Bracken contains the carcinogenic compound ptaquiloside, which causes damage to DNA, thus leading to cancers of the digestive tract. High stomach cancer rates are found in Japan and North Wales, where bracken is often eaten, but it is unclear whether bracken plays a role. Consumption of ptaquiloside-contaminated milk is thought to contribute to human gastric cancer in the Andean states of Venezuela. The spores have also been implicated as carcinogens.However, ptaquiloside is water-soluble and destroyed in heat and alkaline conditions. Korean and Japanese cooks have traditionally soaked the shoots in water and ash to detoxify the plant before eating. Ptaquiloside also degenerates at room temperature, and denatures almost completely at boiling temperature. Despite this, moderation of consumption is still recommended to reduce chances of cancer formation. The British Royal Horticultural Society recommends against consumption of bracken altogether, by both humans and livestock.
Ptaquiloside has been shown to leach from wild bracken plants into the water supply, which has been implicated in high rates of stomach and oesophageal cancers in areas with high bracken growth, such as Wales and South America.
Uncooked bracken also contains the enzyme thiaminase, which breaks down thiamine. Excessive consumption of bracken can lead to vitamin B1 deficiency, especially in animals with simple stomachs. Ruminants are less vulnerable because they synthesize thiamine.
In animals
Ptaquiloside from bracken has been shown to be carcinogenic in some animals. Animals may ingest the plant when other sources of food are unavailable, such as during droughts or after snowfalls.In cattle, bracken poisoning can occur in acute and chronic forms, acute poisoning being the most common. Milk from cows that have eaten bracken may also contain ptaquiloside, which is especially concentrated in buttermilk. In pigs and horses, bracken poisoning induces vitamin B1 deficiency.