Hoary Stinging Nettle

Urtica dioica subsp. holosericea

This month’s plant is one most of us try to avoid. This is because of the trichomes (hairs) that cover its stem and leaves. The hairs have a bulbous base filled with a fluid that when deposited on unprotected skin causes a burning or stinging sensation. Bonnie has drawn a couple of these hairs. It turns out that the irritating fluid is most effective if deposited in a cut. To insure this cut, the sharp point of the hair breaks off leaving a jagged tip which when dragged along the skin results in a tiny cut. While the cut is being made, lateral and/or downward pressure on the hair’s base causes the fluid in the hair to be forced up and out the hollow hair stem to be deposited in the fine cut caused by the broken tip. That is, the stinging hairs are each tiny hypodermic needles.

If you haven’t guessed the plant by now, it’s the true stinging nettle, Urtica dioica subsp. holosericea. Our common or hoary stinging nettle is a subspecies of a very wide ranging species that is found throughout the North American and Eurasian continents. The new Jepson Manual indicates that our subspecies are native. However, the Eurasian subspecies, U. dioica ssp. dioca, is an extremely widespread weed as it has been widely introduced in North America. Apparently there is at least one unconfirmed report of the Eurasian subspecies in California.

So what does one do if one runs into a patch of stinging nettle? My professor in college told us to “wash the itchy area well and then douse it with rubbing alcohol which will cause the itch to disappear in one-half hour.” He would then add, “If you do nothing the itch will go away in 30 minutes.” I’ll let each of you decide whether to treat stinging nettle irritation or not.

Dr. Rhonda Riggins added one additional stinging nettle story. On field trips, when she would find stinging nettle, she would say that she was so strong, that the nettle didn’t bother her. To prove it, she would grab a nettle plant and pull it out. Her students were impressed. However, she had a trick! She was careful to limit her exposure to the palm of her hand where she, as well as most of us, have thick calluses. In other words, the delicate hairs couldn’t penetrate these calluses, so didn’t cause any harm.

Stinging nettles are partial to moist soils and are found most often near streams. They can also be found near springs or in hollows in coastal sand dunes that are low enough to approach the water table. The genus name, Urtica, is derived from Latin and means “to burn” referring to the stinging sensation one receives when brushing up against the plant. I have to admit that I prefer to say the genus name reminds us that to come in contact with this plant (h)urts! Also of note, is that stinging nettle pain begins immediately on contact. This is in contrast to poison oak (Toxicodendron diversiloba) which usually takes ½ hour or more to stimulate your immune system for itching that lasts much longer than ½ hour.

The species epithet, dioica, is short for dioecious. Dioecious is a fancy botanical term for stamens and pistils borne in separate flowers on separate plants, Therefore the plants are considered to be unisexual or bearing either staminate (male) or pistilate (female) flowers but not both.

According to The Jepson Manual our western variety of stinging nettle is the hoary (stinging) nettle. “Hoary” is used in the common name to indicate that this subspecies has many more stinging hairs than the other subspecies found in California.

The common name, nettle, is used for many plants, not just ones possessing stinging hairs. It’s used for any plant that possesses hairs that look like they might sting. Our most common example of this use is the totally unrelated mint, hedge nettle, Stachys bullata.

Hedge nettle is common along streams too. Having spent all these words, telling why you should avoid this plant, I need to point out that the Eurasian subspecies of this plant has been widely used in the old world as a spinach substitute and rennet. Boiling denatures the irritating fluid and softens the hairs. Boiling the roots can produce a yellow dye. Stems produce a strong fiber which has been favorably compared to another stem fiber, linen.

by Dirk Walters, illustrations by Bonnie Walters | Dirk and Bonnie Walters are long-time CNPS-SLO members, contributors, and board/committee participants. In addition to his work at Cal Poly, Dirk is the current CNPS-SLO Historian.