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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]]). 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. 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. 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 [[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. 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. ''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> 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. ==Cultivation== ===Propagation=== ===Pests and diseases=== [[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> == Species == [[Image:Ambrosia-bidentata01.jpg|thumb|right|[[Laceleaf Ragweed]]<br/>''[[Ambrosia bidentata]]'']] [[Image:Ambrosia-tomentosa01.jpg|thumb|right|[[Skeletonleaf Burr Ragweed]]<br/>''[[Ambrosia tomentosa]]'']] * ''[[Ambrosia acanthicarpa]]'' – [[Flatspine Burr Ragweed]], Annual Bursage, Annual Burrweed * ''[[Ambrosia ambrosioides]]'' – [[Ambrosia Burr Ragweed]], Canyon Ragweed, ''chicura'' ** ''Ambrosia ambrosioides'' ssp. ''septentrionale'' * ''[[Ambrosia artemisiifolia]]'' – [[Common Ragweed]], Annual Ragweed, American Wormwood, Blackweed, Carrotweed * ''[[Ambrosia aspera]]'' * ''[[Ambrosia bidentata]]'' – [[Camphor Weed]], [[Lanceleaf Ragweed]] * ''[[Ambrosia camphorata]]'' * ''[[Ambrosia canescens]]'' – [[Hairy Ragweed]] * ''[[Ambrosia carduacea]]'' – [[Baja California Ragweed]] * ''[[Ambrosia chamissonis]]'' – [[Silver Burr Ragweed]], Silver Beachweed, Silver Beach Burr, Beach Bur * ''[[Ambrosia cheirnathifolia]]'' – [[Rio Grande Ragweed]] * ''[[Ambrosia chenopodiifolia]]'' – [[San Diego Burr Ragweed]], San Diego Bursage * ''[[Ambrosia confertiflora]]'' – [[Weakleaf Burr Ragweed]] * ''[[Ambrosia cordifolia]]'' – [[Tucson Burr Ragweed]] * ''[[Ambrosia coronopifolia]]'' * ''[[Ambrosia deltoidea]]'' – [[Triangle Burr Ragweed]], [[Triangleleaf Bursage]], [[Rabbitbush]] * ''[[Ambrosia dumosa]]'' – [[Burrobush]], Burroweed, White Bursage * ''[[Ambrosia eriocentra]]'' – [[Woolly Bursage]], Woollyfruit Burr Ragweed * ''[[Ambrosia grayi]]'' – [[Woollyleaf Burr Ragweed]] * ''[[Ambrosia helenae]]'' * ''[[Ambrosia hispida]]'' – [[Coastal Ragweed]] * ''[[Ambrosia ilicifolia]]'' – [[Hollyleaf Burr Ragweed]], Hollyleaf Bursage * ''[[Ambrosia intergradiens]]'' * ''[[Ambrosia johnstoniorum]]'' * ''[[Ambrosia linearis]]'' – [[Streaked Burr Ragweed]] * ''[[Ambrosia maritima]]'' (the [[type species]]) * ''[[Ambrosia palustris]]'' * ''[[Ambrosia pannosa]]'' * ''[[Ambrosia parvifolia]]'' * ''[[Ambrosia peruviana]]'' – [[Peruvian Ragweed]] * ''[[Ambrosia psilostachya]]'' – [[Western Ragweed]], Cuman Ragweed, Perennial Ragweed * ''[[Ambrosia pumila]]'' – [[Dwarf Burr Ragweed]], San Diego Ambrosia * ''[[Ambrosia sandersonii]]'' * ''[[Ambrosia scabra]]'' ** ''Ambrosia scabra'' var. ''robusta'' ** ''Ambrosia scabra'' var. ''tenuior'' * ''[[Ambrosia tarapacana]]'' * ''[[Ambrosia tenuifolia]]'' – [[Slimleaf Burr Ragweed]] * ''[[Ambrosia tomentosa]]'' – [[Skeletonleaf Burr Ragweed]] * ''[[Ambrosia trifida]]'' – [[Great Ragweed]], Giant Ragweed, Buffalo Weed ** ''Ambrosia trifida texana'' – [[Texan Great Ragweed]] * ''[[Ambrosia trifolia]]'' – [[Greater Ragweed]] * ''[[Ambrosia velutina]]'' ''Ambrosia mexicana'' is actually the [[Jerusalem Oak Goosefoot]] (''Chenopodium botrys''), an entirely unrelated plant. ==Gallery== <gallery perrow=5> File:Ab plant 85.jpg File:Ambrosia 5977.jpg File:Ambrosia gross.jpg File:Ambrosia psilostachya 10446.jpg File:Ambrosia, Croatia.JPG File:Ambrosia-ambrosioides-20080322.JPG File:Ambrosia-deltoides-20080405.JPG Image:Ambrosia chamissonis01.jpg|[[Silver Burr Ragweed]] ''[[Ambrosia chamissonis]]'' 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 --> ==External links== *{{wplink}} {{stub}} __NOTOC__
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