Stinging nettle, pellitory, false nettle
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
If you are a regular reader of my blogs, then you are aware that I have written about a variety of plant species that are principally wind pollinated and which produce pollen grains that act as allergens. These blogs address plants that produce pollen which is included in the daily pollen counts we send to the National Allergy Bureau (NAB). This blog continues in that series and will focus on a family of plants native to our area that has three genera which are known to produce pollen that is often a significant cause of hay fever and asthma. These three genera are Urtica, Parietaria, and Boehmeria, and all flower during the late summer and fall. They grow as weeds in fields and disturbed areas, and the genus Parietaria is planted as an ornamental in many places. These genera produce enormous quantities of pollen that readily become airborne and can comprise a prominent component of the aerospora during the fall.
This family of plants is commonly called the stinging nettle family and is worldwide in its distribution. There are some 45 genera with about 550 species worldwide with six genera found in North America. Of those genera native to the U.S. there are three that are known to produce pollen that possess allergenicity, Urtica, Parietaria, and Boehmeria.
Most members of the Urticaceae family are herbs that possess simple, usually opposite leaves. The stems are usually hairy and occasionally squarish. The flowers are greenish or brownish and the plants are usually dioecious (either male or female flowers on one plant, not both). The ovary is superior in position and has one carpel. Several of the genera in this family have species that possess hairs underneath their leaves that function like hypodermic needles, most notable is the genus Urtica, and which can inject a variety of chemicals into the skin that causes a painful sting; hence the name stinging nettle family. Chemicals injected include histamine, acetylcholine, leukotrienes, serotonin, and possibly formic acid.
Many species in the family are edible, some have medicinal uses, and many have strong fibers that can be used for making cordage. The genus Boehmeria has the longest fibers known in the plant kingdom and these fibers are eight times stronger than cotton fibers. The species, B. nivea, provides the fibers used in production of ramie. These fibers obtained from Boehmeria are called bast fibers and are obtained from the inner bark (the phloem) of the vegetative stalks. Ramie is one of the strongest natural fibers, but it is not very durable and thus is normally mixed with other fibers in the manufacture of cloth or other materials. It is similar to linen in its absorbency but does not dye well. It shows poor elasticity and elongation. B. nivea is native to Asia but is now grown in other regions of the world such as Egypt and parts of South America. The species of Boehmeria found in the Southeastern U.S. is B. cylindrica or false nettle.
Parietaria, common name pellitory or pellitory-of-the-wall, is an herb that is native to Europe and the Mediterranean. It is found throughout the U.S. as a cultivated ornamental. There are several species found in the U.S., including P. floridana and P. officinalis. The plants bear small flowers but produce copious quantities of pollen that is released in “clouds” as the stamens mature and spring upward in the flowers. Pollen grains of Parietaria, like those of Boehmeria and Urtica are small, between 12-15 microns, and have 2-4, usually three pores.
The type genus for this family of plants is Urtica, and the most common species is U. dioica, the common nettle or stinging nettle. This species is native to Europe, Asia, northern Africa, and western North America but has been introduced in many other places and is well established in a worldwide distribution. U. dioica is dioecious and may grow up to seven feet tall during the summer. It is an herbaceous perennial which dies down in the winter but sends up new shoots the following year from underground rhizomes and stolons. The underground portions of the plants are bright yellow. The plant is used for medicinal purposes, particularly for urination problems and enlarged prostate, but also for joint ailments and as a diuretic and astringent. For more information on potential medicinal use of Urtica and other species of Urticaceae go to websites such as WEB MD or the links given below. [Note: As always, I make no claim to the efficacy or use of any plant for medicinal purposes. My blogs are to provide information about various plants and plant families and to encourage you to continue your investigation into the wonderful world of plants.]
As mentioned above, some species in this family are also edible. For additional information on the use of some of the plants in the Urticaceae family as food, see some of the links below or check out books on edible wild plants in a local library or online.
Pellitory-of-the-wall – Parietaria officinalis
False nettle – Boehmeria cylindrica