Uniquely identifiable characteristics.

Distinguishing Feature : the only branched fern.

Bracken can grow to about 8 feet high, and carpet the moorland so densely as to be almost impenetrable to beat a path through should one not already exist. In this state it maintains a high humidity on hot days, and under these conditions it is more likely to harbour sheep ticks. Many, but not all sheep ticks, carry Lime Disease, and if they subsequently bite humans may infect them with this debilitating and in-curable (in its later stages) disease. Any ticks should be removed in their entirety as soon as possible; treatment for Lime Disease is effective provided it is caught within a month of being bitten.

Bracken is a persistent and spreading weed, which will cover vast areas of upland moors if left un-checked by fire or sheep and cattle. Animals will not eat established growth, it is far too un-palatable and poisonous, but they may young shoots. Bracken is clump forming, and digging it up involves great effort for its roots (rhizome) extend quite deep and wide and the root-stock tenacious. And it will re-grow next year anyway. Once established bracken is almost impossible to eradicate unless the area is dug up for several years running. Bracken can be harvested, and is sometimes. But this does little towards eradicating it. The over-wintering undergrowth can become a fire hazard when tinder dry.

The microscopic dust-like spores are carcinogenic and are wafted into the air by summer draughts. There are carcinogens, mainly ptaquiloside, within the plant especially the young 'fiddleheads' and the symptoms of acute lethal poisoning by ingestion of bracken is similar to that from exposure to lethal radiation (for example from a highly radioactive substance): bone marrow aplasia, haemorrhage and severe gastro-intestinal damage. Farm animals are most at risk, especially cattle and sheep. The carcinogens are passed on in the milk from cows, and hence possibly to humans. They can also cause progressive retinal degeneration. The rhizomes are free of ptaquiloside. The concentration of ptaquilosides seems greatest in the Spring, when the young croziers are emerging into fiddleheads.

Bracken is poisonous to livestock if eaten. Sheep are especially vulnerable, as they eat it more often than other animals, who often find it un-palatable unless there is nothing else to eat. In sheep it can cause a condition called bright blindness where the eyes are unable to see, and yet they are not cloudy with glaucoma, the eye remains clear and 'bright'. The bracken destroys the rods and cones in the retina, and their corresponding neurons. Both blood platelet count and white blood cell count is low.

Bracken contains Thiaminase, as do some Horsetails. Thiaminase, if ingested, destroys thiamin (Vitamin B1); clinical signs of poisoning by bracken resemble Vitamin B deficiency, that is beri-beri. Symptoms of vitamin B1 deficiency in beri-beri suffers are severe lethargy and fatigue, as well as plumbing system complications. Death is a possibility. Thiamine (aka Aneurin) is Vitamin B1. Like all vitamins, the body cannot synthesize Thiamine itself and yet requires it, so it has to be provided by the foodstuffs humans eat. [Only Thiamine is shown, which Bracken does not contain; Thiaminase itself is a very large and complicated enzymatic molecule beyond the scope here to depict].

Ptaquiloside, a nor-sesquiterpene with a D-glucose sugar unit attached, is the carcinogenic agent in Bracken. It has a spiro-cyclo-propane unit (shown in red) and it seems to be this that is responsible for the carcinogenicity: it readily opens up and breaks DNA chains most readily wherever the sequence AAAT occurs in the DNA, resulting in DNA cleavage. The young shoots of Bracken have been eaten as a vegetable in Japan resulting in a high incidence of bladder cancer. Ptaquiloside also occurs in a number of other ferns, many of which are foreign to the UK, except Ribbon Fern. If Bracken is consumed by cows, the Ptaquiloside is passed on in the cows' milk. [Ptaquiloside seems to be totally synonymous with Aquiloside A; there seems to be no discernible difference between the two chemical structures. (Not so for Aquiloside B, C, D, etc)]. As well as containing ptaquiloside, other illudane type-B glucosides have been found in bracken, namely Isoptaquiloside and Caudatoside. Ptaquilosin results if the glucose sugar unit (shown in blue) becomes detached from Ptaquiloside. This quickly decomposes again to Pterosin B, or the DNA Adduct. Pterosin B is one of a number of indanone products synthesized in Bracken. Some of these Indanones, Illudin A and Illudin B (which also have a spiro-cyclopropane unit) have also been found in the poisonous mushroom Jack-o-Lantern (Omphalotus illudens)

MODUS OPERANDUS OF THE CARCINOGEN PTAQUILOSIDE Ptaquiloside, has a spiro-cyclo-propane unit (shown in red) which readily opens up and breaks DNA chains most readily wherever the sequence AAAT occurs in the DNA, resulting in DNA cleavage. Ptaquiloside is unstable under both acidic and basic conditions, and readily hydrolyses with water to produce first Ptaquilosin (losing the sugar unit), then a number of Pterosins. And yet it is not the Pterosins which cause the damage to cells, it is the proximity of DNA to Ptaquilosin which can precipitate the decomposition of Ptaquilosin forming a DNA Adduct via intermediary compounds not shown instead of Pterosin B. The DNA Adduct then goes on to synthesize the wrong proteins, causing havoc in the cell. Thus Ptaquiloside is both mutagenic and carcinogenic, and is ultimately responsible for most of the carnage wreaked upon a mammal by consumption of Bracken. But not all. There are other poisons and carcinogens present, Kaempferol amongst them. It has not been proved that Ptaquiloside is the carcinogen in the spores, which are also carcinogenic. As an aside, the Author speculates: Rather than ptaquiloside (and other chemicals that plants produce that interfere with DNA/RNA) being a means by which to poison external enemies of plants, might not these be utilised in some way by the plant itself to control or influence some aspect of its' own development? Although it may seem a little like putting a 'spanner in a gearbox' sort of mechanism, could this be just what the plant needs in certain circumstances, for instance when the plant is damaged? When a leaf, or a branch needs to fall off? Or perhaps much more subtle and purposful changes, like the anther splits into two at this juncture? After all, all plants are different in non-subtle ways. These DNA disruptive chemicals might be just the ticket the plant needs to co-ordinate different aspects of itself. This cannot be a universal mechanism utilised by all plants; not all plants produce ptaquiloside for a start, but a lot of plants do produce other carcinogenic chemicals. Carcinogens usually act upon DNA/RNA mechanisms. Could many plants have invented diverse methods for controlling some aspect of themselves? After all, a fern is not a grass. This individualistic nature may explain why such a mechanism has remained obscure; bilogists tend to study universal mechanisms rather than exclusive processes. Have we discovered all there is to find out about what makes all species, genera and families different? The Author will leave the reader to further ponder and speculate upon this matter. He doesn't know the answer.

CHLORINE-CONTAINING PTEROSINS In addition to other pterosins, Bracken contains three chlorine-containing pterosins, Pterosin F (which Chameleon also contains) Pterosin H and Pterosin K, all closely related.

Bracken contains the related carcinogens Quercetin and Kaempferol, both of which are flavonoids, and in this case, flavonols. They are polyphenolic plant anti-oxidants, also known as Catechins. Quercetin is found in a wide variety of plants such citrus fruits and onions. Kaempferol has one less hydroxyl group than Quercetin and is found in Beans, Grapefruit, Brussel Sprouts, Broccoli, Apples, Witch-Hazel and Delphiniums. Rutin is a diglucoside of Kaempferol, also found in a variety of different plants. Kaempferitrin and Astragalin are other glucosides of Kaempferol. Flavonols are yellow or deep yellow in colour and contribute to the colour of many yellow flowers.

TYPICAL MODUS OPERANDI OF CYANOGENIC GLUCOSIDES Bracken contains the cyanogenic glucoside Prunasin (albeit in this instance in harmless quantities). Prunasin is a dangerously poisonous cyanogenic glucoside which is also present in Black Cherry (Rum Cherry, Prunus serotina) and in Cherry Laurel (Prunus laurocerasus). Cyanogenic glucosides contain (one or more) glucosides ('sugar' molecules) attached to a cyanide group somehow. Examples of other naturally occurring cyanogenic glucosides are Amygdalin, Unamarin, Lotaustralin, Sambunigrin, Dhurrin, Taxiphyllin, Linamarin and Heterodendrin. After ingestion, the cyanogenic glucoside is acted upon by hydrolysing enzymes (which are themselves liberated from the plant cells after ingestion), releasing first the sugar molecule (and in the case of Prunasin) leaving Mandelonitrile. Mandelonitrile is further acted upon by the hydrolysing enzymes releasing Benzaldehyde and Hydrogen Cyanide. Similar mechanisms are at work for the other cyanogenic glucosides; the end result always being that hydrogen cyanide is released. It is the hydrogen cyanide which is the poisonous fraction; that preferentially binds to haemoglobin in the blood preventing oxygen from binding. The consequence, if sufficient is consumed, is death by lack of oxygen (asphyxiation). Thus the plant needs to contain both the cyanogenic glucoside as well as the hydrolysing enzyme to be poisonous, if it contains just the latter, it is none poisonous. The highest amounts of Prunasin in Bracken (which are found mainly in the fronds and spores) occurs in the spring-time when it is growing fastest (whilst it is in the crozier stage). A great many plants contain Cyanogenic glucosides, including Cassava (tapioca), and many plants belonging to the Rose Family, Pea Family, Spurge Family, Carrot Family and the Grasses etc. Sea Arrow-grass contains the cyanogenic glucoside Taxiphyllin, Elder contains the Cyanogenic glucoside Sambunigrin, which is the (S-)-enantiomer of Prunasin. The cyanogenic glucosides themselves are synthesized within the plants from various amino acids, and are there to protect the plant from herbivores. It is possible that valuable anti-cancer drugs may be derived from the many and varied cyanogenic glucosides by engineering the delivery system to target cancer cells, thus delivering the HCN directly to the cancerous cells rather than poisoning haemoglobin. Some other Cyanogenic Glycosides liberate a third molecule besides hydrogen cyanide, such as acetone or metylethylketone. See Cultivated Flax.

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