project reflections #26

Burn Weed

It is my hope that it has now become apparent to the reader how many of the pioneering plants that I have thus far described employ – by means of adaptation – various ingenious biological defenses against the animals that might eat them.

These defenses constitute the great armoury of spines, thorns, prickles, bristles – and bitter, unsavory compounds and poisonous concoctions – that botanical nature has designed and brewed up to deter animal interest, investigation, and ingestion.In terms of our human experience of these arms and fortifications, there can surely be no more commonly suffered strategy than the sting of the common nettle – Urtica dioica. Every child – and every parent – must surely be conscious of that shockingly unpleasant ‘first contact’ with this painful weed; of the alarming white bumps and reddened skin that we associate with ‘nettle rash’.

Stinging nettle or common nettle, Urtica dioica, is a herbaceous perennial flowering plant, native to Europe, Asia, northern Africa and North America – it is the best-known member of the genus Urtica. The plant has many hollow stinging hairs called trichomes on its leaves and stems, which act like hypodermic needles; injecting histamine and other chemicals that produce a stinging sensation when contacted by humans and other animals. The plant has a long history of use as a medicine and as a food source.

Stinging nettle is a dioecious herbaceous perennial, 1 to 2 m (3 to 7 ft) tall in the summer and dying down to the ground in winter. It has widely spreading rhizomes and stolons, which are bright yellow, as are the roots. The soft green leaves are 3 to 15 cm (1 to 6 in) long and are borne oppositely on an erect wiry green stem. The leaves have a strongly serrated margin, a cordate base, and an acuminate tip with a terminal leaf tooth longer than adjacent laterals. It bears numerous small, greenish or brownish flowers in dense axillary inflorescences.

The leaves and stems are very hairy with non-stinging hairs and they also bear many stinging hairs (trichomes), whose tips come off when touched, transforming the hair into a needle that will inject several chemicals: acetylcholine, histamine, 5-HT (serotonin), moroidin, leukotrienes, and – possibly – formic acid. This mixture of chemical compounds causes a painful sting or paresthesia from which the species derives its common name, as well as the colloquial names: burn nettle, burn weed, burn hazel.

Urtication, or flogging with nettles, is the process of deliberately applying stinging nettles to the skin in order to provoke inflammation. An agent thus used is known as a rubefacient (something that causes redness). This is done as a folk remedy for rheumatism, providing temporary relief from (or at least a novel replacement for) pain in the joints.

As Old English stiðe, nettle is one of the nine plants invoked in the pagan Anglo-Saxon Nine Herbs Charm, recorded in the 10th century. Nettle was believed to be a galactagogue, a substance that promotes lactation.

Because it contains 3,4-divanillyltetrahydrofuran, certain extracts of the nettle are used by bodybuilders in an effort to increase free testosterone.

An annual Stinging Nettle Eating Championship draws thousands of people to Dorset, where competitors attempt to eat as much of the raw plant as possible. Competitors are given 60 cm (20 in) stalks of the plant, from which they strip the leaves and eat them. Whoever strips and eats the most stinging nettle leaves in a fixed time is the winner. The competition dates back to 1986, when two neighbouring farmers attempted to settle a dispute about which had the worst infestation of nettles.

In Europe stinging nettles have a strong association with human habitation and buildings. The presence of nettles may indicate that a building has been long abandoned. Human and animal waste may be responsible for elevated levels of phosphate and nitrogen in the soil, providing an ideal environment for stinging nettles.

Paul Evans, February 2012

One thought on “project reflections #26

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s