Ragweed

Created 1999.

Common name: Common ragweed, wild tansy, hog weed, Roman wormwood, wild tansy, bitterweed, mayweed, hay fever weed, black weed, Roman wormweed, annual ragweed.
Botanical name: Ambrosia species, esp A. artemisiifolia. A genus of over 40 species.
Family: Asteraceae
Origin: They are native to the temperate regions of North and South America. Ambrosia spp. were imported to Europe during the mid 20th century as contaminants in seed. Ragweed is only known in N.Z. as a casual and seed impurity, but is commonly found in Australia. They prefer dry, grassy plains, particularly along riverbanks and roadsides. They often thrive in disturbed soils, such as on vacant lots.
Description: The plant has fine, soft hairs on the stem and on both sides of the leaves. They vary in colour from light green to greenish- magenta. Depending on the growing conditions, it can grow from between a few centimeters to over a meter in height. The flowers are very small, yellow-green in colour. Each plant is reputed to be able to produce over a billion grains of pollen over a season. The plants bloom in the northern hemisphere from mid August until cooler weather arrives. On dry windy days, the pollen will travel many kilometers.
Uses: A weed
Allergens: The major hay fever allergen has been identified as a 38 kDa nonglycosylated protein. In addition, Ragweed contains Profilin and Calcium++-binding proteins. The skin allergens include a variety of sesqueterpene lactones.
Allergy: Worldwide, ragweed is arguably the most common cause of hay fever. Two species, A. artemisiifolia and A. psilostachya are considered particularly noxious. Contact with the plant can also cause allergic contact dermatitis, particularly amongst gardeners and farmers. Contact with the plant can also cause allergic contact dermatitiss, particularly amongst gardeners and farmers.
Cross reactions: Ragweed pollen cross react with almost all other compositea pollens, especially with mugwort pollen. The sesqueterpene lactones also can cross react with dandelion, goldenrod, sun flower, chamomile, and most other daisy-like flowers. Western Ragweed, naturalised to Australia, is reported to cross react with turpentine.
Other information: The name of this genus is derived from the Greek word for “food of the gods’. Ragweed is a plant of concern in the global warming issue, because tests have shown that higher levels of carbon dioxide will greatly increase pollen production. When the humidity rises above 70%, the pollen tends to clump and is not so likely to become airborne.
Patch test: Sesquiterpene lactone. Specific IgE to Ragweed pollens.

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