Difference between revisions of "Ambrosia"

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{{SPlantbox
 
{{SPlantbox
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|familia=Asteraceae
 
|genus=Ambrosia
 
|genus=Ambrosia
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|poisonous=highly allergenic pollen
 
|Temp Metric=°F
 
|Temp Metric=°F
 
|jumpin=If this plant info box on watering; zones; height; etc. is mostly empty you can click on the edit tab and fill in the blanks!
 
|jumpin=If this plant info box on watering; zones; height; etc. is mostly empty you can click on the edit tab and fill in the blanks!
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|image=Upload.png
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|image=Western ragweed.jpg
 
|image_width=240
 
|image_width=240
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|image_caption=Ambrosia
 
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{{Inc|
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'''Ragweeds''' ('''''Ambrosia'''''), also called '''bitterweeds''' or '''bloodweeds''', are a [[genus]] of flowering [[plant]]s from the sunflower [[family (biology)|family]] ([[Asteraceae]]).
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Ambrosia (a classical name). Compositae. About fifteen species of weedy evil-smelling herbs, mostly American. The common ragweed is A. artemisiaefolia, Linn. The kingweed of western wheatfields, and also of low waste places, is A. trifida, Linn. Probably none is cultivated, the listed Ambrosia mexicana probably being of some other genus, very likely an artemisia.
 
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}}
 
  
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{{Taxobox
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The scientific name of this genus is sometimes claimed to be derived from the [[Ancient Greek]] term for the perfumed nourishment of the gods, ''[[ambrosia]]'', which would be ironic, since the genus is best known for one fact: its [[pollen]] produces severe and widespread [[allergies]]. However, the [[name of a biological genus|generic name]] is actually [[cognate]] with the name of the divine dish, both being derived from ''ambrotos'' (άμβροτος), "[[immortality|immortal]]". In the case of the plants, this aptly refers to their tenaciousness, which makes it hard to rid an area of them if they occur as [[invasive weed]]s.
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| color = lightgreen
 
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| name = Common Ragweed
 
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| image = Ambrosia_5977.jpg
 
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| image_width = 250px
 
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| image_caption = Ambrosia
 
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| regnum = [[Plant]]ae
 
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| divisio = [[Flowering plant|Magnoliophyta]]
 
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| classis = [[Magnoliopsida]]
 
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| ordo = [[Asterales]]
 
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| familia = [[Asteraceae]]
 
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| tribus = [[Heliantheae]]
 
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| genus = '''''Ambrosia'''''
 
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| genus_authority = [[Carolus Linnaeus|L.]], [[1753]]
 
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| subdivision_ranks = Species
 
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| subdivision =
 
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See text.
 
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}}
 
  
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'''Ragweeds''' (''Ambrosia'') is a genus of flowering plants from the sunflower family ([[Asteraceae]]).  
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Ragweeds occur in [[temperate]] regions of the [[Northern Hemisphere]] and [[South America]]. Ragweeds prefer dry, sunny grassy plains, sandy soils, [[river]] banks, roadsides, and [[ruderal species|ruderal sites]] (disturbed soils) such as vacant lots and abandoned fields.
  
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The name of this genus is derived from the Greek word for "food of the gods".
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There are 41 [[species]] worldwide. Many are adapted to the [[arid]] climates of the [[desert]]. [[Burrobush]] (''A. dumosa'') is one of the most arid-adapted perennials in [[North America]]. About 10 species occur in the [[Sonoran Desert]].
  
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They occur in [[temperate]] regions of the northern hemisphere and South America. They prefer dry, sunny grassy plains; sandy soils; and to grow along [[river]] banks, along roadsides, disturbed soils, vacant lots and ruderal sites. Ragweed was far less common in the Eastern United States before dense European settlement/agriculture in the late 1700s.  
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This genus is not to be confused with ''[[Kochia scoparia]]'', which also has the [[common name]] "ragweed".
  
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[[Image:Ambrosia chamissonis01.jpg|thumb|left|Silver Burr ragweed (''Ambrosia chamissonis'')]]  
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Ragweeds are [[annual plant|annuals]], [[perennial plant|perennials]], and [[shrub]]s and [[subshrub]]s (called '''bursages'''), with erect, [[hispid]] [[Plant stem|stems]] growing in large clumps to a height of usually {{nowrap|75-90 cm}}. The stems are basally branched. They form a slender [[taproot]] or a creeping [[rhizome]]. [[Common Ragweed]] (''A. artemisifolia'') is the most widespread of this genus in [[North America]]. It attains a height of about a meter. Great Ragweed (''[[Ambrosia trifida]]'') may grow to four meters ({{nowrap|13 feet}}) or more.
  
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There are 41 [[species]] worldwide. They are very ordinary in appearance. Despite being all around, they are easily overlooked. Virtually no animal browses them. Many are adapted to the arid climates of the [[desert]]. Burrobush (''Ambrosia dumosa'') is one of the most arid-adapted perennials in North America. About 10 species occur in the Sonoran Desert.
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The [[foliage]] is grayish to silvery green with [[bipinnatifid]], deeply lobed [[Leaf|leaves]] with winged petioles; in the case of ''[[Ambrosia coronopifolia]]'', the leaves are simple. The leaf arrangement is opposite at the base but becomes alternate higher on the stem.
  
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These are [[annual plant|annuals]], [[perennial plant|perennials]] and [[shrub]]s and subshrubs with erect, hispid [[Plant stem|stems]] growing in large clumps to a height of 75 - 90 cm. The stems are basally branched. They form a slender [[taproot]] or a creeping [[rhizome]].
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''Ambrosia'' is a [[monoecious]] plant, i.e., it produces separate male and female flower heads on the same plant. The numerous tiny male [[inflorescences]] are yellowish-green disc flowers about {{nowrap|3 mm}} in diameter. They grow in a terminal spike, subtended by joined [[bract]]s. The whitish-green single female flowers are inconspicuously situated below the male ones, in the leaf axils. A [[pappus (flower structure)|pappus]] is lacking.<ref>Payne (1963)</ref>
  
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The [[foliage]] is grayish to silvery green with bipinnatifid, deeply lobed [[Leaf|leaves]] with winged petioles. But in the  case of ''Ambrosia coronopifolia'', the leaves are simple. The leaf arrangement is opposite at the base, but becomes alternate higher on the stem.
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After [[anemophily|wind pollination]], the female flower develops into a prickly, ovoid burr with 9-18 straight spines. It contains one arrowhead-shaped seed, brown when mature, and smaller than a wheat grain. This burr gets dispersed by clinging to the fur or feathers of animals passing by.  
  
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Ragweeds are used as food plants by the [[larva]]e of a number of [[Lepidoptera]] species, see [[list of Lepidoptera which feed on ragweeds]].
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==Cultivation==
  
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[[Image:Ambrosia.jpg|thumb|left|Annual Ragweed (''Ambrosia artemisiifolia'')]]
 
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==Reproduction==
 
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Ambrosia is a monoecious plant, i.e. it produces separate male and female flower heads on the same plant. The numerous tiny male, yellowish-green disc flower are about 3 mm in diameter. They grow in a terminal spike,  subtended by joined [[bract]]s. The female, whitish-green flowers are 1-flowered and are inconspicuously  situated below the male ones,  in the leaf axils. The pappus is lacking.
 
  
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After [[anemophily|wind pollination]], the female flowers develops into a prickly, ovoid burr with 9-18 straight spines. It contains one arrowhead-shaped seed, brown when mature, and smaller than a wheat grain.  This burr gets dispersed by clinging to the fur or feathers of animals passing by. The seeds are an important winter food for many bird species.
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===Propagation===
  
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==Allergen==
 
  
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Each plant is reputed to be able to produce about a billion grains of [[pollen]] over a season, and the plant is anemophilous (wind-[[pollination|pollinated]]). It is highly allergenic, as the greatest pollen [[allergen]] of all pollens, and the prime cause of [[hayfever]]. The [[plant]] blooms in the northern hemisphere from about mid August until cooler weather arrives. It usually produces pollen more copiously in wet seasons. Two species, ''Ambrosia artemisiifolia'' and ''A. psilostachya'' are considered among the most noxious to those prone to hay fever.
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===Pests and diseases===
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[[Rust (fungus)|Fungal rust]]s and especially the leaf-eating beetle ''Ophraella communa'' have been proposed for [[biological control]] to be used against ragweed, but the latter may be dangerous to [[sunflower]]s and there have been problems obtaining permits and funding to test such controls.<ref>Kiss pp. 83-89</ref>
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Common Ragweed (''Ambrosia artemisiifolia'') is the most widespread of this genus in [[North America]]. It attains a height of about a meter. Great Ragweed, Giant Ragweed or Horseweed, (''Ambrosia trifida''), may grow to four meters (13 feet) or more.
 
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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. On dry windy days, the pollen will travel many kilometers. When the humidity rises above
 
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70%, the pollen tends to clump and is not so likely to become airborne.
 
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[[Goldenrod]] is frequently blamed for hayfever, but simply happens to have a showy [[flower]] that blooms about the same time. Goldenrod is innocent, as it is [[entomophily|entomophilous]], ie. [[insect]] pollinated. Its pollen is heavy and sticky, and cannot become airborne.
 
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Some high mountain and desert areas of North America used to be refuges for severe hay fever sufferers, who would go to such areas for relief during the pollen season, but increased human activity such as building and other disturbances of the soil, irrigation, and gardening, have encouraged ragweed to spread to these areas as well. Today, no area in the [[United States]] is ragweed pollen free, and moving can only offer a degree of relief. The ragweed was accidentally imported to Europe during [[World War I]], it had adapted to the different environment successfully and has greatly spread since the 1950s. [[Hungary]] is currently the most heavily affected country in Europe (and possibly the entire world), especially since the early 1990s, when abandonment of communist-style collective agriculture left vast fields uncultivated, which were promptly invaded by ragweed.
 
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Anecdotal claims are made of [[honey]] giving some relief for ragweed pollen [[allergy|allergies]], which is noteworthy because [[honeybee]]s very rarely visit ragweed flowers, and even then only for pollen. However, during ragweed pollen shed, the pollen dusts every surface, and honeybees, being electrostatically charged, will accumulate some ragweed pollen. The pollen is frequently [[Melissopalynology|identified]] as a component of raw honey.
 
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The major allergen protein has been [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16254437&query_hl=19&itool=pubmed_docsum identified] as [[Amb a 1]], a 38 k[[Atomic mass unit|Da]] nonglycosylated [[protein]].
 
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==Control and Eradication==
 
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Total eradication of ragweed is considered impossible, owing to the plant's frugality and tremendous seed-producing capability. As of 2005, there is no known safe biological remedy (e.g. beetle or worm) to be used against ragweed in the open. Mechanical and chemical methods are available and can be used to control its spread, although there is evidence that these are actually no more effective than leaving the weed alone, in the long run[http://links.jstor.org/sici?sici=0040-9618%28197311%2F12%29100%3A6%3C333%3ARCTEOO%3E2.0.CO%3B2-C&size=LARGE].
 
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The act of manually uprooting ragweeds, sometimes shown in the media for public awareness and propaganda purposes, is best avoided. It is ineffective, and skin contact may cause the onset of full-blown hayfever symptoms in persons with latent ragweed hyper-sensitivity.
 
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Although the [[scythe]] and its motorized descendants have a reduced efficiency against ragweed, they remain indispensable tools, especially in populated areas and near delicate plantation, where herbicide use must be limited. Fighting ragweed with the scythe is a continuous process, because it is difficult to cut the plant right at the soil level, and the plant will regrow in two weeks (and often branch into three or four full-sized stems) if more than half an inch of the plant remains above the ground. Areas where ragweed has been reaped should be mowed down every three weeks to prevent regrowth.
 
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It is considered important to control the spread of ragweed in large abandoned or uncultivated areas. Ragweed pollen can remain airborne for days and travel great distances, affecting people hundreds of miles away. One efficient method for large-scale ragweed extermination is chemical spraying. Because ragweed only reacts to some of the more aggressive herbicides, it is highly recommended to consult professionals when deciding on dosage and methodology, especially near urban areas. Some proven effective active ingredients include those that are gliphosat-based (Roundup, Gliphogan, Glialka), sulphosat-based (Medallon) and gluphosinat-ammonia based (Finale14SL). In badly infested areas u
 
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sually 2 to 6.5 [[liters]] of herbicides are dispersed per [[hectare]] (equal to app. 0.2 to 0.7 US [[gallon]]s per [[acre]]).
 
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One especially effective method of controlling ragweed; cutting it, then burning it once the stalks have dried[http://links.jstor.org/sici?sici=0040-9618(197311%2F12)100%3A6%3C333%3ARCTEOO%3E2.0.CO%3B2-C] (standing, live ragweed won't burn) has become less popular because the smoke produced is seen as unacceptable pollution, as with the decline in leaf-burning and trash burning. But this method has the added benefit of killing off the stems so the plant does not grow back, which (as noted above) is otherwise almost inevitable.
 
  
 
== Species ==
 
== Species ==
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[[Image:Ambrosia2.jpg|thumb|right|250px|Annual Ragweed (''Ambrosia artemisiifolia'' ) - leaves]]
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[[Image:Ambrosia-bidentata01.jpg|thumb|right|[[Laceleaf Ragweed]]<br/>''[[Ambrosia bidentata]]'']]
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* ''[[Ambrosia acanthicarpa]]'' : Flatspine Burr Ragweed, Annual Bur-Sage
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[[Image:Ambrosia-tomentosa01.jpg|thumb|right|[[Skeletonleaf Burr Ragweed]]<br/>''[[Ambrosia tomentosa]]'']]
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* ''[[Ambrosia ambrosioides]]'' : Ambrosia Burr Ragweed, Canyon Ragweed
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* ''[[Ambrosia acanthicarpa]]'' &ndash; [[Flatspine Burr Ragweed]], Annual Bursage, Annual Burrweed
 +
* ''[[Ambrosia ambrosioides]]'' &ndash; [[Ambrosia Burr Ragweed]], Canyon Ragweed, ''chicura''
 
** ''Ambrosia ambrosioides'' ssp. ''septentrionale''  
 
** ''Ambrosia ambrosioides'' ssp. ''septentrionale''  
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* ''[[Ambrosia artemisiifolia]]'' : Annual Ragweed, Bitterweed, Blackweed, American Wormwood
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* ''[[Ambrosia artemisiifolia]]'' &ndash; [[Common Ragweed]], Annual Ragweed, American Wormwood, Blackweed, Carrotweed
 
* ''[[Ambrosia aspera]]''  
 
* ''[[Ambrosia aspera]]''  
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* ''[[Ambrosia bidentata]]'' : Camphor Weed, Lanceleaf Ragweed
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* ''[[Ambrosia bidentata]]'' &ndash; [[Camphor Weed]], [[Lanceleaf Ragweed]]
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* ''[[Ambrosia canescens]]'' : Hairy Ragweed
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* ''[[Ambrosia camphorata]]''
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* ''[[Ambrosia carduacea]]'' : Baja California Ragweed
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* ''[[Ambrosia canescens]]'' &ndash; [[Hairy Ragweed]]
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* ''[[Ambrosia chamissonis]]'' : Silver Burr Ragweed, Silver Beachweed, Silver Beach Burr
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* ''[[Ambrosia carduacea]]'' &ndash; [[Baja California Ragweed]]
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* ''[[Ambrosia cheirnathifolia]]'' : Rio Grande Ragweed
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* ''[[Ambrosia chamissonis]]'' &ndash; [[Silver Burr Ragweed]], Silver Beachweed, Silver Beach Burr, Beach Bur
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[[Image:Ambrosia-artemisiifolia01.jpg|thumb|right|250px|Annual Ragweed (''Ambrosia artemisiifolia'') - flowers]]
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* ''[[Ambrosia cheirnathifolia]]'' &ndash; [[Rio Grande Ragweed]]
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* ''[[Ambrosia chenopodiifolia]]'' : San Diego Burr Ragweed, San Diego Burr Sage.
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* ''[[Ambrosia chenopodiifolia]]'' &ndash; [[San Diego Burr Ragweed]], San Diego Bursage
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* ''[[Ambrosia confertiflora]]'' : Weakleaf Burr Ragweed
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* ''[[Ambrosia confertiflora]]'' &ndash; [[Weakleaf Burr Ragweed]]
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* ''[[Ambrosia cordifolia]]'' : Tucson Burr Ragweed
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* ''[[Ambrosia cordifolia]]'' &ndash; [[Tucson Burr Ragweed]]
 
* ''[[Ambrosia coronopifolia]]''
 
* ''[[Ambrosia coronopifolia]]''
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* ''[[Ambrosia deltoidea]]'' : Triangle Burr Ragweed, Triangleleaf Bur-sage, Rabbitbush.
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* ''[[Ambrosia deltoidea]]'' &ndash; [[Triangle Burr Ragweed]], [[Triangleleaf Bursage]], [[Rabbitbush]]
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* ''[[Ambrosia dumosa]]'' : Burrobush, White Bursage.
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* ''[[Ambrosia dumosa]]'' &ndash; [[Burrobush]], Burroweed, White Bursage
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* ''[[Ambrosia elatior]]'' (synonym of ''A. artemisiifolia''): Carrotweed, Annual Ragweed
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* ''[[Ambrosia eriocentra]]'' &ndash; [[Woolly Bursage]], Woollyfruit Burr Ragweed
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* ''[[Ambrosia grayi]]'' : Woollyleaf Burr Ragweed
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* ''[[Ambrosia grayi]]'' &ndash; [[Woollyleaf Burr Ragweed]]
 
* ''[[Ambrosia helenae]]''
 
* ''[[Ambrosia helenae]]''
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* ''[[Ambrosia hispida]]'' : Coastal Ragweed
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* ''[[Ambrosia hispida]]'' &ndash; [[Coastal Ragweed]]
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* ''[[Ambrosia ilicfolia]]'' : Hollyleaf Burr Ragweed, Hollyleaf Bursage.
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* ''[[Ambrosia ilicifolia]]'' &ndash; [[Hollyleaf Burr Ragweed]], Hollyleaf Bursage
 
* ''[[Ambrosia intergradiens]]''
 
* ''[[Ambrosia intergradiens]]''
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* ''[[Ambrosia johnstoniorum]]''  
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* ''[[Ambrosia johnstoniorum]]''
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* ''[[Ambrosia linearis]]'' : Streaked Burr Ragweed
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* ''[[Ambrosia linearis]]'' &ndash; [[Streaked Burr Ragweed]]
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* ''[[Ambrosia maritima]]'' : type species
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* ''[[Ambrosia maritima]]'' (the [[type species]])
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[[Image:Ambrosia-acanthicarpa.jpg|thumb|right|250px|Flatspine Burr ragweed (''Ambrosia acanthicarpa'')]]
 
 
* ''[[Ambrosia palustris]]''  
 
* ''[[Ambrosia palustris]]''  
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* ''[[Ambrosia pannosa]]''  
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* ''[[Ambrosia pannosa]]''
 
* ''[[Ambrosia parvifolia]]''  
 
* ''[[Ambrosia parvifolia]]''  
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* ''[[Ambrosia peruviana]]'' : Peruvian Ragweed
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* ''[[Ambrosia peruviana]]'' &ndash; [[Peruvian Ragweed]]
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* ''[[Ambrosia psilostachya]]'' : Cuman Ragweed, Western Ragweed, Perennial Ragweed
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* ''[[Ambrosia psilostachya]]'' &ndash; [[Western Ragweed]], Cuman Ragweed, Perennial Ragweed
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* ''[[Ambrosia pumila]]'' : Dwarf Burr Ragweed, San Diego Ambrosia
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* ''[[Ambrosia pumila]]'' &ndash; [[Dwarf Burr Ragweed]], San Diego Ambrosia
 
* ''[[Ambrosia sandersonii]]''  
 
* ''[[Ambrosia sandersonii]]''  
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* ''[[Ambrosia scabra]]''  
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* ''[[Ambrosia scabra]]''
 
** ''Ambrosia scabra'' var. ''robusta''  
 
** ''Ambrosia scabra'' var. ''robusta''  
 
** ''Ambrosia scabra'' var. ''tenuior''  
 
** ''Ambrosia scabra'' var. ''tenuior''  
 
* ''[[Ambrosia tarapacana]]''  
 
* ''[[Ambrosia tarapacana]]''  
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* ''[[Ambrosia tenuifolia]]'' : Slimleaf Burr Ragweed
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* ''[[Ambrosia tenuifolia]]'' &ndash; [[Slimleaf Burr Ragweed]]
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* ''[[Ambrosia tomentosa]]'' : Skeletonleaf Burr Ragweed
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* ''[[Ambrosia tomentosa]]'' &ndash; [[Skeletonleaf Burr Ragweed]]
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* ''[[Ambrosia trifida]]'' : Great Ragweed, Giant Ragweed, Bitterweed, Bloodweed
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* ''[[Ambrosia trifida]]'' &ndash; [[Great Ragweed]], Giant Ragweed, Buffalo Weed
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** ''Ambrosia trifida texana'' : Texan great Ragweed
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** ''Ambrosia trifida texana'' &ndash; [[Texan Great Ragweed]]
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* ''[[Ambrosia trifolia]]'' : Bitterweed, Bloodweed, Great Ragweed, Buffalo Weed
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* ''[[Ambrosia trifolia]]'' &ndash; [[Greater Ragweed]]
 
* ''[[Ambrosia velutina]]''
 
* ''[[Ambrosia velutina]]''
  
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==External links==
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''Ambrosia mexicana'' is actually the [[Jerusalem Oak Goosefoot]] (''Chenopodium botrys''), an entirely unrelated plant.
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*[http://herbarium.uvsc.edu/Virtual/search.asp?s=genus&p=1&n=695&t=Ambrosia UVSC Herbarium - Ambrosia]
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* {{cite journal | author = Wopfner N, Gadermaier G, Egger M, Asero R, Ebner C, Jahn-Schmid B, Ferreira F | title = The spectrum of allergens in ragweed and mugwort pollen. | journal = Int Arch Allergy Immunol | volume = 138 | issue = 4 | pages = 337-46 | year = 2005 | month=Dec | id = PMID 16254437 | url=http://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=IAA2005138004337 | doi= 10.1159/000089188}}
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==Gallery==
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* {{cite journal | author = Payne WW | title = The Morphology of the Inflorescence of Ragweeds (Ambrosia-Franseria: Compositae) | journal = American Journal of Botany | volume = 50 | issue = 9 | pages = 872-880 | year = 1963 | month=Oct | url=http://www.jstor.org/view/00029122/di001617/00p0112h/0}}
 
  
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<gallery perrow=5>
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File:Ab plant 85.jpg
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File:Ambrosia 5977.jpg
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File:Ambrosia gross.jpg
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File:Ambrosia psilostachya 10446.jpg
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File:Ambrosia, Croatia.JPG
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File:Ambrosia-ambrosioides-20080322.JPG
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File:Ambrosia-deltoides-20080405.JPG
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Image:Ambrosia chamissonis01.jpg|[[Silver Burr Ragweed]] ''[[Ambrosia chamissonis]]''
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Image:Starr_010222-9001_Ambrosia_artemisiifolia.jpg|[[Common Ragweed]] ''Ambrosia artemisiifolia''
 +
</gallery>
  
 +
==References==
 +
<references/>
 +
*[[Standard Cyclopedia of Horticulture]], by L. H. Bailey, MacMillan Co., 1963
 +
<!--- xxxxx  *Flora: The Gardener's Bible, by Sean Hogan. Global Book Publishing, 2003. ISBN 0881925381  -->
 +
<!--- xxxxx  *American Horticultural Society: A-Z Encyclopedia of Garden Plants, by Christopher Brickell, Judith D. Zuk. 1996. ISBN 0789419432  -->
 +
<!--- xxxxx  *Sunset National Garden Book. Sunset Books, Inc., 1997. ISBN 0376038608  -->
  
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[[Image:Ambrosia-bidentata01.jpg|thumb|left|225px|Laceleaf Ragweed (''Ambrosia bidentata'')]]
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==External links==
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[[Image:Ambrosia-tomentosa01.jpg|thumb|left|225px|Skeletonleaf Burr Ragweed (''Ambrosia tomentosa'')]]
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*{{wplink}}
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[[Image:Ambrosia-trifida02.jpg|thumb|right|225px|Great Ragweed (''Ambrosia trifida'')]]
 
  
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[[Category:Asteraceae]]
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{{stub}}
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[[Category:Pollination]]
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__NOTOC__
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[[Category:Allergology]]
 

Latest revision as of 20:46, 12 January 2010


Ambrosia


Plant Characteristics
Poisonous: ☠ highly allergenic pollen
Cultivation
Scientific Names

Asteraceae >

Ambrosia >


If this plant info box on watering; zones; height; etc. is mostly empty you can click on the edit tab and fill in the blanks!


Ragweeds (Ambrosia), also called bitterweeds or bloodweeds, are a genus of flowering plants from the sunflower family (Asteraceae).

The scientific name of this genus is sometimes claimed to be derived from the Ancient Greek term for the perfumed nourishment of the gods, ambrosia, which would be ironic, since the genus is best known for one fact: its pollen produces severe and widespread allergies. However, the generic name is actually cognate with the name of the divine dish, both being derived from ambrotos (άμβροτος), "immortal". In the case of the plants, this aptly refers to their tenaciousness, which makes it hard to rid an area of them if they occur as invasive weeds.

Ragweeds occur in temperate regions of the Northern Hemisphere and South America. Ragweeds prefer dry, sunny grassy plains, sandy soils, river banks, roadsides, and ruderal sites (disturbed soils) such as vacant lots and abandoned fields.

There are 41 species worldwide. Many are adapted to the arid climates of the desert. Burrobush (A. dumosa) is one of the most arid-adapted perennials in North America. About 10 species occur in the Sonoran Desert.

This genus is not to be confused with Kochia scoparia, which also has the common name "ragweed".

Ragweeds are annuals, perennials, and shrubs and subshrubs (called bursages), with erect, hispid stems growing in large clumps to a height of usually Template:Nowrap. The stems are basally branched. They form a slender taproot or a creeping rhizome. Common Ragweed (A. artemisifolia) is the most widespread of this genus in North America. It attains a height of about a meter. Great Ragweed (Ambrosia trifida) may grow to four meters (Template:Nowrap) or more.

The foliage is grayish to silvery green with bipinnatifid, deeply lobed leaves with winged petioles; in the case of Ambrosia coronopifolia, the leaves are simple. The leaf arrangement is opposite at the base but becomes alternate higher on the stem.

Ambrosia is a monoecious plant, i.e., it produces separate male and female flower heads on the same plant. The numerous tiny male inflorescences are yellowish-green disc flowers about Template:Nowrap in diameter. They grow in a terminal spike, subtended by joined bracts. The whitish-green single female flowers are inconspicuously situated below the male ones, in the leaf axils. A pappus is lacking.[1]

After wind pollination, the female flower develops into a prickly, ovoid burr with 9-18 straight spines. It contains one arrowhead-shaped seed, brown when mature, and smaller than a wheat grain. This burr gets dispersed by clinging to the fur or feathers of animals passing by.

Cultivation

Propagation

Pests and diseases

Fungal rusts and especially the leaf-eating beetle Ophraella communa have been proposed for biological control to be used against ragweed, but the latter may be dangerous to sunflowers and there have been problems obtaining permits and funding to test such controls.[2]

Species

Laceleaf Ragweed
Ambrosia bidentata
Skeletonleaf Burr Ragweed
Ambrosia tomentosa

Ambrosia mexicana is actually the Jerusalem Oak Goosefoot (Chenopodium botrys), an entirely unrelated plant.

Gallery

References

  1. ↑ Payne (1963)
  2. ↑ Kiss pp. 83-89

External links


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