Family: Nettle Family (Urticaceae)
Origin and Distribution: Stinging nettle is a bristly, stinging perennial that is extremely variable in its morphology. Two varieties exist in North America. The most common variety (Urtica dioica var. procera) is native, while an uncommon and more bristly type (Urtica dioica var. dioica) was introduced from Europe, possibly for use as greens. It is difficult to distinguish between American and European varieties; however, the introduced variety is rarely encountered. Stinging nettle is widespread throughout the eastern U.S. and in most counties in Ohio. This weed thrives in damp, nutrient-rich soil and does not grow well where soil nutrients, especially phosphorus, are low. It can be found in pastures, nurseries, orchards, neglected yards, waste places, roadsides, flood plains, stream banks and ditches, as well as along the edges of fields and woodlots where it tolerates partial shade. This species does not tolerate saline conditions.
Plant Description: Stinging nettle is an erect, herbaceous perennial that is widely known for its unpleasant stinging hairs on the stems and lower leaf surface. It reproduces by wind-dispersed seeds and creeping rhizomes (horizontal underground stems), and grows in dense clumps, often forming large colonies.
- Root system - Stinging nettle has an extensive underground network of rhizomes (horizontal underground stems) that can spread 5 feet or more in a season. Fibrous roots are produced along the rhizomes.
- Seedlings & Shoots - Cotyledons are oval, with a notch at the tip. The first leaves are opposite, oval to egg-shaped, thin and bright green. The toothed margins of the first few leaves are more rounded than in older plants. Young leaves and stems are covered with hairs and a few stinging hairs.
- Stems - Stems are mostly unbranched, and grow 3 to 6 1/2 feet tall (sometimes up to 9 feet). They are covered with bristly stinging hairs (fewer in the upper part of the stem), and otherwise, are smooth or have a few soft hairs. Stems are slender and approximately square in cross section.
- Leaves - The thin, bright to dark green leaves are opposite, with saw-toothed margins and infamous stinging hairs on the underside. Leaves are broadly to narrowly egg-shaped (2 to 6 inches long, 1 to 2 inches wide), with a rounded or heart-shaped base and a pointed tip. Aside from the stinging hairs, the upper and lower leaf surfaces are usually smooth (the lower surface may be slightly hairy). Pointed stipules (small leaf-like appendages) occur at the base of the leaf, but senesce early. Leaf stalks are 1/4 to 2/3 the length of the leaf.
- Flowers - Tiny, greenish-white flowers are arranged in clusters on slender, branched spikes formed in the leaf axils (usually 4 spikes per node). Male and female flower clusters are produced on the same plant (monoecious), but usually from different leaf axils. Male flower spikes are longer than female flower spikes.
- Fruits & Seeds - Stinging nettle produces a small, dry, oval-shaped, 1-seeded fruit (achene) that is yellow to grayish-tan. Fruits are clustered along drooping flower spikes.
Similar Species: The uncommon European variety of stinging nettle (Urtica dioica var. dioica or Urtica dioica spp. dioica, often referred to simply as Urtica dioica; European stinging nettle, common nettle, hokey pokey, devil's leaf, naughty man's plaything) is more branched and sprawling, with more densely hairy leaves and stinging hairs abundant on stems and both leaf surfaces. Leaves of the European variety are much broader and heart-shaped. Unlike the native stinging nettle, the European type is dioeceous, meaning its male and female flowers are found on separate plants. Small stinging nettle seedlings might be confused with mints, which also have opposite, serrated leaves and square stems, but no stinging hairs.
Biology: Flowers of stinging nettle are produced between May and October, and are wind-pollinated. A greater proportion of early season flowers are male, while flowers in the summer are predominantly female. Over 20,000 seeds can be produced on a single plant growing in the sun. Seeds remain attached to the spikes until frost, and have little or no dormancy. Because seeds lack dormancy, germination can occur soon after seeds are shed, but most germination is seen in early spring when soil temperatures are above 40° F. Seeds can live 10 or more years in the soil.
Stinging nettle has an extensive underground network of rhizomes that facilitate spread, as well as regrowth in springtime or following mowing. New plants are often established from rhizome fragments that have been spread by machinery.
The weediness of stinging nettle is attributed to its spread by rhizomes, allowing it to form dense colonies that exclude other species. Eradicating an established colony is difficult because the subterranean system expands yearly and cannot be suppressed by mowing. This species does not compete well with grasses, but is able to establish and spread among legumes or other forbs. Stands of stinging nettle are thought to persist for 50 years. Distribution of this species is limited by its intolerance of poor fertility, dense shade and frequent disturbance. Some control may be obtained through repeated tillage and cultivation over several years.
Toxicity: Stinging hairs on the stem and leaves of stinging nettle cause irritation upon contact with skin. The toxins are located at the base of each stinging hair. When skin brushes against the stinging hairs, the bulbous tip of each hair readily breaks off, forming a sharp shaft that acts like a hypodermic needle to inject the toxins into the skin, causing localized pain, reddish swelling, itching and numbness. Toxins thought to be involved include formic acid (also found in ants), histamine, acetylcholine and 5-hydroxytryptamine. The symptoms caused by these chemicals will last for a few minutes to a few hours, and then resolve on their own. Airborne pollen, which is shed in large amounts when stinging nettle is in flower, is an important contributor to hay fever.
Facts and Folklore:
- Relief from stinging nettle's burn comes by rubbing inflamed skin with juice from the leaves of dock, jewelweed, rosemary, mint, sage or even crushed leaves of stinging nettle itself!
- The fiber in stinging nettle stems is very similar to that of hemp and flax, and for this reason, has historically been an important ingredient in a variety of items, from sailcloth and fishing nets to clothing and paper.
- Europeans cook stinging nettle, removing the stinging hairs by boiling, and find it a good source of vitamins A and C, protein and iron.
- Pulling up stinging nettle by the roots while calling out a sick person's name was believed to drive away a fever.
- Urtication, the process of beating the skin with nettles, was formerly used to treat certain diseases.
- Hunting dogs have died from extreme exposure to stinging nettle.