Dwarf Nettle (not native)

In early spring, bright green patches of dwarf nettle (Urtica urens) line the shady trails in San Elijo Ecological Reserve. With their neatly scalloped leaves, they make a pleasant sight. Unfortunately, dwarf nettle has the same bad disposition as it’s close cousin, stinging nettle. Both plants are covered with stiff, hollow hairs that contain a chemical cocktail of irritants; this is injected into the skin when the plant is brushed. Dwarf nettle has been called the most painful plant in the United States.

Ironically, the sap of dwarf nettle has been recommended as a remedy for the sting. Perhaps that is the origin of this old English rhyme:

  Tender-handed, stroke a nettle.
  And it stings you for your pains.
  Grasp it like a man of mettle,
  And it soft as silk remains.

Description ^4,11,59,240

Dwarf nettle is a short-lived annual, usually less than 30 inches (75 cm) high, with one to several stems arising from the base. The stems are more square than round, often grooved, and green or sometimes reddish in color. The bright green leaves are paired along the stem, elliptical to oval and usually less than 2 1/2 inches (6 cm) long; the regular scalloping along the margins is characteristic. Leaves contain crystals of calcium carbonate (cystoliths) that appear as tiny bumps on the leaf surface. All parts of the plant have numerous small hairs, the larger of which are sharp, stiff and hollow, with a bulbous base. These hairs act as miniature hypodermic needles. They are filled with a cocktail of histamines, acetylcholine, serotonin, and formic acid. When brushed, the tips are broken and pressure within the hairs forces the chemicals out of the tip and into the skin, causing itching, swelling, and burning.

Flowers are tiny, crowded and difficult to interpret, even with a microscope. Flowers are unisexual. Male and female flowers occur together in short, compound clusters arising from the leaf axils. There are neither petals nor nectar glands. Male flowers are symmetrical with four sepals and four stamens which extend outward when the sepals open; the white anthers provide the only color and make the male flowers easier to spot. There is a rudimentary pistil. Female flowers have two pairs of sepals, the inner being slightly larger than the outer. The ovary is superior with a tufted stigma. Female flowers are compressed and have the appearance of clam shells. The main bloom period in January – April.⁷

Each ovary produces a single small, flattened seed, protected by persistent inner sepals.

Classification ^11,23,143

Dwarf nettle is a member of the nettle family (Urticaceae). Plants in this family often have stinging hairs. Inconspicuous flowers are born in short clusters from leaf axils and are often either male or female. Neither have petals. Male flowers have four sepals and four stamens and a rudimentary pistil. Female flowers have two pairs of unequal sepals and a simple ovary that develops one seed.

The gentle baby tears (Soleirolia soleirolii) of shady gardens belong to this family.

In the Reserve, we have five members of the nettle family.⁴⁸ In addition to dwarf nettle, there are two other stinging species: stinging nettle (U. dioica) and Western nettle (Hesperocnide tenella). Non-stinging western pellitory (Parietaria hespera) and the non-native baby tears have also been found.

Ecology

Dwarf nettle is considered by some to be the most painful plant in the United States.⁵⁶ The stinging hairs protect the plant from herbivores. In turn, the nettle provides refuge for small insects which can exist on the plant without becoming rabbit food.²⁴⁰ Nettles are important host plants for several of our butterflies including Painted Lady, West Coast Lady, and Red Admiral.^116,244 These insects are eaten primarily by small birds, thereby adding another link to the nettle-food-web.^41,240

Dwarf nettle lacks both petals and nectar glands, the two most common means of attracting pollinating insects. Instead, flowers are wind-pollinated. The filaments are folded inward in the developing bud. When the sepals part, the filaments spring outward, flinging the pollen away from the plant.²⁴¹

Human Uses

In spite of their impressive sting, nettles have been used for a variety of purposes for hundreds of years. For culinary and medicinal uses, dwarf nettle and stinging nettle are interchangeable.^41,213

Nettle is very nutritious and often found at Farmer’s markets. The sting is deactivated by boiling or drying and pulverizing.^56,242Some recommend using only the young plants,⁷¹or plants before they bloom.²⁴² After this time the crystoliths begin to form and are reputed to irritate the digestive tract and even damage the kidneys.^92,242

A wide variety of nettle recipes – from tea to lasagne – are available on the web (just google “nettle recipes”). Although livestock avoid the fresh plants, dried nettles make a nutritional forage.^92,241

Nettles have been used medicinally since medieval times and continue to be important in modern alternative medicine. Folk medicine recommended nettles to cure everything from the bite of a mad dog and hemlock poisoning, to asthma and rheumatism.⁹²The latter two uses persist today in Alternative Medicines as treatments for hay fever and osteoarthritis.²¹³ One of the most curious folk remedies is to apply the sap of the plant to counteract its sting.^56,92,242

Interesting Facts

May 14-25, 2008 was “Be nice to Nettles Week” in England.²⁴⁰