During a recent wildflower hike in the Ivy Creek Natural Area outside Charlottesville our group came across a common fern, likely the most prolific of the plants that make up the division Pteridophyta. It is found on every continent except Antarctica, and in every environment except those desiccated from lack of rainfall. Imagine our surprise when our guide informed us that this fern is now thought to be one of the most carcinogenic on earth! OK, so it’s not just mushrooms we have to be wary of eating.
It’s common name is Bracken Fern and is sometimes called “weed fern” because of its’ habit of choking out any other plants and forming a dense impenetrable thatch. In Britain it is considered invasive and steps have been taken to eradicate it because of its’ encroachment on pasture land. The bracken has a very successful “rhizome” structure. 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.
A second reason for the dominance of the bracken fern over its competitors is the chemical compounds excreted by the plant that inhibit the growth of other plants. Some of those chemicals are ptaquiloside, a lactone toxin that affects the bone marrow and is probably carcinogenic, and cyanogenic glycosides that yield hydrogen cyanide.
The newly emerging fronds of the bracken fern, called “fiddleheads”, are commonly gathered in the spring and eaten fresh. They are considered a delicacy, particularly in Japan and Korea. Bracken’s toxicity to grazing animals has long been known. The symptoms start with a condition known as “bracken staggers” as the muscles degenerate. Untreated, death can result in less than a fortnight; the antidote is daily injections of thiamine.
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.
Sources: British Journal of Cancer
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