Ragweed

Ragweeds are flowering plants in the genus ''Ambrosia'' in the aster family, Asteraceae. They are distributed in the tropical and subtropical regions of the Americas, especially North America,''Ambrosia''
Flora of North America. where the origin and center of diversity of the genus are in the southwestern United States and northwestern Mexico. Several species have been introduced to the Old World and some have naturalized and have become invasive species. In Europe, this spread is expected to continue, due to ongoing climate change.

The name "ragweed" is derived from "ragged" + "weed," coming from the ragged appearance of the plant's leaves. Other common names include bursages''Ambrosia''
Integrated Taxonomic Information System (ITIS). and burrobrushes.''Ambrosia''
The Jepson eFlora 2013. The genus name is from the Greek ''ambrosia'', meaning "food or drink of immortality".

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.

The most widespread species of the genus in North America is ''Ambrosia artemisiifolia''.

Description and ecology

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.

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. The pistillate flowers are wind pollinated,Genus ''Ambrosia''
Arizona-Sonora Desert Museum. and the fruits develop. They are burs, sometimes adorned with knobs, wings, or spines.

Many ''Ambrosia'' species occur in desert and semi-desert areas, and many are ruderal species that grow in disturbed habitat types.

Allergy

Ragweed pollen is a common allergen. A single plant may produce about a billion grains of pollen per season,Rees, A. M. ''Consumer Health USA: Essential Information from the Federal Health Network'' 2nd ed. Volume 2. Westwood, Connecticut: Greenwood, 1997. pg. 32. "Each ragweed plant produces about one billion pollen grains during an average allergy season". 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. Common culprits are common ragweed (''A. artemisiifolia'') and great ragweed (''A. trifida'').

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. Ragweed pollen can remain airborne for days and travel great distances, and can even be carried out to sea. 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. 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.

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.

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 of certain fruits, vegetables, and nuts. Foods commonly involved include beans, celery, cumin, hazelnuts, kiwifruit, parsley, potatoes, bananas, melons, cucumber. 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.

Merck & Co, under license from allergy immunotherapy (AIT) company ALK, has launched a ragweed allergy immunotherapy treatment in sublingual tablet form in the US and Canada.

As of 2006, research into allergy immunotherapy treatment involved administering doses of the allergen to accustom the body to induce specific long-term tolerance.

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. 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.

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. 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.

Species

There are about 50 species in genus ''Ambrosia''. Species include:''Ambrosia''
The Plant List.

* '' Ambrosia acanthicarpa'' Hook. – flatspine bur ragweed, annual bursage, sand bursage
* '' Ambrosia acuminata'' (Brandegee) W.W.Payne
* '' Ambrosia ambrosioides'' (Cav.) W.W.Payne – ambrosia-leaf bur ragweed, big bursage, ambrosia bursage
* '' Ambrosia arborescens'' Mill. – marko, altamisa
* ''Ambrosia artemisiifolia'' L. – common ragweed, short ragweed, Roman wormwood
* '' Ambrosia artemisioides'' Meyen & Walp.
* '' Ambrosia bidentata'' Michx. – lanceleaf ragweed, southern ragweed
* '' Ambrosia bryantii'' (Curran) Payne
* '' Ambrosia camphorata'' (Greene) W.W.Payne
* '' Ambrosia canescens'' A.Gray – hairy ragweed
* '' Ambrosia carduacea'' (Greene) W.W.Payne
* '' Ambrosia chamissonis'' (Less.) Greene – silver burr ragweed, beach-bur
* '' Ambrosia cheiranthifolia'' A.Gray – Rio Grande ragweed, South Texas ambrosia
* '' Ambrosia chenopodiifolia'' (Benth.) W.W.Payne – San Diego bur ragweed, San Diego bursage
* '' Ambrosia confertiflora'' DC. – weakleaf bur ragweed
* '' Ambrosia cordifolia'' (A.Gray) W.W.Payne – Tucson bur ragweed, heartleaf bursage
* '' Ambrosia deltoidea'' (Torr.) W.W.Payne – triangle bur ragweed, triangle bursage
* '' Ambrosia dentata'' (Cabrera) M.O.Dillon
* '' Ambrosia divaricata'' (Brandegee) Payne
* '' Ambrosia diversifolia'' (Piper) Rydb.
* '' Ambrosia dumosa'' (A.Gray) W.W.Payne – burrobush, white bursage
* '' Ambrosia eriocentra'' (A.Gray) W.W.Payne – woolly fruit bur ragweed, hollyleaf bursage
* '' Ambrosia flexuosa'' (A.Gray) W.W.Payne
* '' Ambrosia grayi'' (A.Nelson) Shinners – woollyleaf bur ragweed, lagoonweed
* ''Ambrosia'' × ''helenae'' Rouleau – Helen ragweed
* '' Ambrosia hispida'' Pursh – coastal ragweed
* '' Ambrosia humi'' León de la Luz & Rebman
* '' Ambrosia ilicifolia'' (A.Gray) W.W.Payne – hollyleaf bur ragweed
* ''Ambrosia'' × ''intergradiens'' W.H.Wagner – intergrading ragweed
* '' Ambrosia johnstoniorum'' Henrickson
* '' Ambrosia linearis'' (Rydb.) W.W.Payne – streaked bur ragweed
* '' Ambrosia magdalenae'' (Brandegee) W.W.Payne
* '' Ambrosia maritima'' L.
* '' Ambrosia microcephala'' DC.
* '' Ambrosia monogyra'' (Torr. & A.Gray) Strother & B.G.Baldwin – singlewhorl burrobrush
* '' Ambrosia nivea'' (B.L.Rob. & Fernald) W.W.Payne
* '' Ambrosia pannosa'' W.W.Payne
* '' Ambrosia peruviana'' Willd. – ragweed, altamisa
* ''Ambrosia'' × ''platyspina'' (Seaman) Strother & B.G.Baldwin
* '' Ambrosia polystachya'' DC.
* ''Ambrosia psilostachya'' DC. – Cuman ragweed, western ragweed, perennial ragweed
* '' Ambrosia pumila'' (Nutt.) A.Gray – dwarf bur ragweed, San Diego ambrosia
* '' Ambrosia salsola'' (Torr. & A. Gray) Strother & B.G. Baldwin
* '' Ambrosia scabra'' Hook. & Arn.
* '' Ambrosia tacorensis'' Meyen
* '' Ambrosia tarapacana'' Phil.
* '' Ambrosia tenuifolia'' Spreng. – slimleaf bur ragweed, lacy ambrosia
* '' Ambrosia tomentosa'' Nutt. – skeletonleaf bur ragweed
* '' Ambrosia trifida'' L. – great ragweed, giant ragweed
* '' Ambrosia velutina'' O.E.Schulz
* '' Ambrosia villosissima'' Forssk.

References

External links

*

GRIN Species Records of ''Ambrosia''
. Germplasm Resources Information Network (GRIN).

{{Taxonbar, from=Q844270

Allergology
Ruderal species
Taxa named by Carl Linnaeus