The name "ragweed" is derived from "ragged" + "weed," coming from the ragged appearance of the plant's leaves.[5] Other common names include bursages[6] and burrobrushes.[7] The genus name is from the
Greekambrosia, meaning "food or drink of immortality".[2]
Ragweed
pollen is notorious for causing
allergic reactions in humans, specifically
allergic rhinitis. Up to half of all cases of pollen-related allergic rhinitis in North America are caused by ragweeds.[8]
Ragweeds are
annual and
perennial herbs and
shrubs. Species may grow just a few centimeters tall or exceed four meters in height. The stems are erect, decumbent or prostrate, and many grow from
rhizomes. The leaves may be arranged alternately, oppositely, or both. The leaf blades come in many shapes, sometimes divided pinnately or palmately into lobes. The edges are smooth or toothed. Some are hairy, and most are glandular.[2]
Ragweeds are
monoecious, most producing
inflorescences that contain both staminate and pistillate flowers. Inflorescences are often in the form of a spike or
raceme made up mostly of staminate flowers with some pistillate clusters around the base. Staminate flower heads have
stamens surrounded by whitish or purplish florets. Pistillate flower heads have fruit-yielding
ovules surrounded by many
phyllaries and fewer, smaller florets.[2] The pistillate flowers are
wind pollinated,[9][10] and the fruits develop. They are
burs, sometimes adorned with knobs, wings, or spines.[2]
Many Ambrosia species occur in
desert and semi-desert areas, and many are
ruderal species that grow in disturbed habitat types.[3]
Allergy
Ragweed pollen is a common
allergen. A single plant may produce about a billion grains of pollen per season,[11][12] and the pollen is transported on the wind. It causes about half of all cases of pollen-associated allergic rhinitis in North America, where ragweeds are most abundant and diverse.[8] Common culprits are
common ragweed (A. artemisiifolia) and
great ragweed (A. trifida).[13]
Concentration of ragweed pollen—in the absence of significant rainfall, which removes pollen from the air, is the lowest in the early morning hours (6:00 AM), when emissions starts. Pollen concentration peaks at midday.[14] Ragweed pollen can remain airborne for days and travel great distances, and can even be carried 300–400 miles (500–600 km) out to sea.[12] Ragweeds native to the Americas have been introduced to Europe starting in the nineteenth century and especially during
World War I, and have spread rapidly since the 1950s.[15] Eastern Europe, particularly
Hungary, has been badly affected by ragweed since the early 1990s, when the dismantling of Communist collective agriculture led to large-scale abandonment of agricultural land, and new building projects also resulted in disturbed, un-landscaped areas.[16]
The major allergenic compound in the pollen has been identified as Amb a 1, a 38 k
Da nonglycosylated protein composed of two
subunits. It also contains other allergenic components, such as
profilin and
calcium-binding proteins.[17]
Ragweed allergy sufferers may show signs of
oral allergy syndrome, a food allergy classified by a cluster of allergic reactions in the mouth in response to the consumption certain fruits, vegetables, and nuts.[18] Foods commonly involved include
beans,
celery,
cumin,
hazelnuts,
kiwifruit,
parsley,
potatoes,
bananas,
melons,
cucumbers, and
zucchini. Because cooking usually
denatures the proteins that cause the reaction, the foods are more allergenic when eaten raw; exceptions are celery and nuts, which may not be safe even when cooked. Signs of reaction can include itching, burning, and swelling of the mouth and throat, runny eyes and nose,
hives, and, less commonly, vomiting, diarrhea,
asthma, and
anaphylaxis. These symptoms are due to the abnormal increase of IgE antibodies which attach to a type of immune cell called mast cells. When the ragweed antigen then attaches to these antibodies the mast cells release histamine and other symptom evoking chemicals.[19]
As of 2006, research into allergy immunotherapy treatment involved administering doses of the allergen to accustom the body to induce specific long-term tolerance.[20]
Control and eradication
Where herbicides cannot be used, mowing may be repeated about every three weeks, as it grows back rapidly. In the past, ragweed was usually cut down, left to dry, and then burned.[21] This method is used less often now, because of the
pollution caused by smoke. Manually uprooting ragweed is generally ineffective, and skin contact can cause allergic reaction. If uprooting is the method of choice, it should be performed before flowering. There is evidence that mechanical and chemical control methods are actually no more effective in the long run than leaving the weed in place.[21]
Fungal rusts and the leaf-eating beetle Ophraella communa have been proposed as agents of
biological pest control of ragweeds, but the latter may also attack
sunflowers, and applications for permits and funding to test these controls have been unsuccessful.[22] The beetle has, however, appeared in Europe, either on its own or as an uncontrolled introduction, and it has started making a dent into
Ambrosia populations there.[23][24][25][26]
Species
There are about 50 species in genus Ambrosia. Species include:[27]
^Samter, M. and D. W. Talmage. Immunological Diseases 3rd ed. Volume 2. Boston: Little Brown. 1978. pg. 788.
ISBN0-316-76985-1 "It is estimated that a single plant produces 1 billion shafts of pollen, or that 1 square mile of ragweed plants produces 16 tons of pollen".
^
abRees, A. M. Consumer Health USA: Essential Information from the Federal Health Network 2nd ed. Volume 2. Westwood, Connecticut: Greenwood, 1997. pg. 32.
ISBN1-57356-068-5 "Each ragweed plant produces about one billion pollen grains during an average allergy season".
^Barnes, Charles; Pacheco, Freddy; Landuyt, Julie; Hu, Frank; Portnoy, Jay (2001). "Hourly variation of airborne ragweed pollen in Kansas City". Annals of Allergy, Asthma & Immunology. 86 (2): 166–71.
doi:
10.1016/S1081-1206(10)62686-5.
PMID11258685.
^Kiss, L. "Spread of Common Ragweed in Europe: An Example for Biological Invasion Caused by an Alien Weed Introduced to a New Environment". In: Vincent, C., et al. Biological Control: A Global Perspective. Wallingford, Oxon.: CABI. 2007. pg. 81.
ISBN1-84593-265-X
^
abLewis, Alan J. (1973). "Ragweed Control Techniques: Effect on Old-Field Plant Populations". Bulletin of the Torrey Botanical Club. 100 (6): 333–8.
doi:
10.2307/2484099.
JSTOR2484099.