Ragweed (Ambrosia spp.)
General Information
Ragweed is a hay fever plant that is a member of the genus Ambrosia, which is part of the Asteraceae family. Ragweed is an annual or perennial herbs with lobed or divided leaves. They range from small plants 6 to 8 inches in height to giant plants, which can be 12 feet tall. There are 21 species of ragweed that grow in North America, but most allergy problems are caused by two species: Ambrosia artemisiifolia (short ragweed) and Ambrosia trifida (giant ragweed). These two species produce pollen that cause more hay fever than all other plants combined. Ragweed is monoecious, meaning the staminate (male parts) and pistillate (female parts) flowers are produced on the same plant.

Short Ragweed (Ambrosia artemisiifolia)
Short ragweed is also known as common ragweed. The leaves of common ragweed are 4 to 10 cm long and are hairy. The seedling stems below cotyledons. Their seedlings are green, usually spotted with purple and their cotyledons are roundish to oblong and are purple underneath. The stems are branched with long rough hairs. The flower heads of common ragweed are small, green and arranged in slender stalks at the end of branches. Male and female flowers are in separate heads on the same plant. The roots of this weed are shallow taproot and the fruits are woody achenes that are yellow to reddish brown in color.
Short ragweed, Ambrosia artemisiifolia
Short ragweed, Ambrosia artemisiifolia, Flower
Short ragweed, fruits

Giant Ragweed (Ambrosia trifida)
Giant ragweed is annual plant that grows 3 to 12 feet in height and branches occasionally. The stems of giant ragweed are green and are covered with white hairs. The opposite leaves are up to 12" long and 8" across. The larger leaves are divided into 3 or 5 lobes, usually serrated along the margins, and have long petioles that are sometimes winged. There are smaller leaves near the base of the plant that usually have a hairy underneath. Many of the upper stems end in a cylindrical spike of flowers. These flowers are a yellowish green and lack both petals and sepals. The seeds are large, tough-coated, and remain viable in the soil for several years. The root system is fibrous.

Giant ragweed, Ambrosia trifida
Giant ragweed, Flowers
Giant ragweed, Mature fruit

Asteraceae Family
Plantae – Plants
Tracheobionta – Vascular plants
Spermatophyta – Seed plants
Magnoliophyta – Flowering plants
Magnoliopsida – Dicotyledons
Asteraceae – Aster family
Ambrosia L. – ragweed

The Asteraceae family is also known as the Compositae family, and is generally referred to as aster, daisy or composite family. This particular family has more than 1,600 genera and almost 24,000 species of herbs, shrubs, and trees distributed throughout the world. Asteraceae is one of the largest plant families and is known for its many garden ornamentals, such as ageratums, asters, chrysanthemums, cosmos, dahlias, marigolds and zinnias. Besides ragweed, weeds that fall under the Asteraceae family are dandelion and thistle. Other plants in this family that are economically important for the products derived from their seeds, leaves or tubers are artichoke, endive, safflower, salsify, lettuce, sunflower, and wormwood. Members of the family have flower heads composed of many small flowers, called florets that are surrounded by bracts (leaf like structures). The sepals have been reduced to a ring of hairs, scales, or bristles that is called the pappus on the mature fruit. The one-seeded fruits of this family are achene, which has a hard outer covering.

Geographic Distribution
Ragweed can be found worldwide, but is most prevalent in North America. The only state that does not have ragweed is Alaska. Other areas where ragweed can be found are South America, Europe, Japan, Taiwan, and Australia.
Distribution of Ragweed


To view the global distribution of Ambrosia artemisiifolia, click here.

Human Uses and Domestication
Native Americans used fibers from the stems to make thread. Some believed chewing the roots would alleviate fear at night. The Cherokee used giant ragweed for several medicinal uses, including as a pulmonary aid. They also crushed the leaves to rub on insect stings. Although it was once used for these medical purposes, ragweed is now considered an allergen that causes allergic reactions in those who are affected. Also, people have not domesticated ragweed. Ragweed is a weed that is capable of growing in many places such as in pastures, low woods, forests, along creeks, railroads and in waste areas. Not only is ragweed a nuisance to allergy sufferers, but also it is a nuisance to farmers. Giant ragweed can cause yield reductions up to 35% in corn and 50% in soybeans when in crop fields; therefore, farmers spray herbicides to limit ragweed's growth.

Additional Aspect
What is ragweed allergy?
The immune system is a system of specialized cells and organs that defend the body from foreign invaders such as bacteria, viruses, fungi, and parasites. In order to defend the body from these substances, the immune system must be able to distinguish between "self" and "non-self." When foreign, "non-self," substances are detected, the immune system responds with cells that either attack the substance or produce proteins, called antibodies, that bind to the substance. A substance that is capable of triggering an immune response is called an antigen. In some people, harmless substances, such as ragweed, are considered a threat and cause the immune system to generate an allergic response. When the immune system produces an allergic response, the antigens are known as allergens. These allergic reactions are inherited disorders, meaning the human tendency to develop allergies is determined by genetics.

People with allergies have sensitive immune systems that react when they come in contact with certain allergens, such as ragweed. When people who are allergic to ragweed pollen inhale its allergens from air, hay fever symptoms develop. The common symptoms of hay fever are eye irritation, runny nose, stuffy nose, puffy eyes, sneezing, and inflamed, itchy nose and throat. For those with severe allergies, asthma attacks, chronic sinusitis, headaches and impaired sleep are symptoms.

Who suffers from ragweed allergy?
Of Americans who are allergic to pollen-producing plants, 75 percent are allergic to ragweed. People with allergies to one type of pollen tend to develop allergies to other pollens as well. Typically, 10 to 20 percent of Americans begin to suffer from ragweed allergy, or hay fever.

How is the allergy diagnosed?

The diagnosis of ragweed allergy requires a careful medical history, a physical exam and testing. To confirm a suspected allergy, a skin sensitivity test is used. The skin sensitivity test involves the skin being scratched or pricked with extract of ragweed pollen. In sensitive people, the site will turn red, swollen and itchy. Sometimes blood tests are used to see if an antibody to ragweed is present.

How is ragweed allergy treated?
There is no cure for ragweed allergy. The best way to control the allergy is to avoid the problem, meaning avoid contact with ragweed pollen. However, it is difficult to avoid contact with ragweed since it is so prevalent. Some suggestions to control the allergy are as follows:
  • Track the pollen count in your neighborhood
  • Stay indoors in central air conditioning
  • Take antihistamine medications
    • When you are exposed to an allergen, like ragweed pollen, it triggers your immune system to go into action. Immune system cells known as "mast cells" release a substance called histamine, which attaches to receptors in blood vessels causing them to enlarge. Histamine also binds to other receptors causing redness, swelling, itching, and changes in secretions. By blocking histamine receptors, antihistamines prevent these symptoms.
    • Over-the-counter antihistamines
      • Benadryl, Claritin, Zyrtec
    • Prescription antihistamines
      • Clarinex, Allegra
  • If medication does not provide enough relief, consider immunotherapy, which are allergy shots

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