western ragweed

(Ambrosia psilostachya)

Conservation Status
western ragweed
 
  IUCN Red List

not listed

     
  NatureServe

N4N5 - Apparently Secure to Secure

SNR - Unranked

     
  Minnesota

not listed

     
           
Wetland Indicator Status
     
  Great Plains

FACU - Facultative upland

     
  Midwest

FACU - Facultative upland

     
  Northcentral & Northeast

FAC - Facultative

     
           
 
Description
 
 

Western ragweed is a 12 to 40, usually 12 to 24 tall, erect, perennial forb that rises from creeping, fibrous roots and rhizomes. It is colonial, often forming dense patches. The root system releases chemical toxins that inhibit the growth or germination of nearby competing plants (allelopathy).

The stems are erect, bushy, branched at least above the middle, and covered with white hairs.

Leaves are opposite near the base, alternate above. They are narrow and once pinnatifid, the lobes deep, widely spaced, and bluntly pointed. They are ¾ to 5½ long, usually no longer than 2, and to 2 wide, usually no wider than 1. The upper and lower surfaces are rough to the touch, gland-dotted, and covered with stiff hairs that are either straight or appressed. The leaves near the base are on stalks up to 1 long, the stalks progressively shorter as they ascend the stem. Upper leaves are attached to the stem without stalks.

There are separate male and female flowers, both borne on the same plant. Male flowers are borne in spike-like inflorescences at the ends of stems and branches. The spikes are up to 4 long with 5 to 30, usually 5 to 15 flower heads. The heads are green, bead-like, and about in diameter. They hang downward at the end of short stalks. Female flowers appear singly from upper leaf axles. Both flowers are rayless and have no floral scent.

The fruit is an achene without tufts of hair.

 
     
 

Height

 
 

12 to 40, usually 12 to 24

 
     
 

Flower Color

 
 

Green

 
     
 

Similar Species

 
 

Common ragweed (Ambrosia artemisiifolia) leaves are bipinnatifid (twice cut), not pinnatifid (once cut).

Giant ragweed (Ambrosia trifida) is a much taller plant. Its leaves are palmately lobed.

Lance-leaved ragweed (Ambrosia bidenta) leaves, as the latin name suggests, have two teeth, one on each side of the leaf. It has been recorded only in Ramsey County.

Annual bursage (Ambrosia acanthicarpa) leaves are bipinnatifid and are covered with white to gray, short, bristly hairs.

 
     
 
Habitat
 
 

Dry. Prairies, disturbed sites.

 
     
 
Ecology
 
 

Flowering

 
 

August to September

 
     
 

Pests and Diseases

 
 

Olive-shaded bird-dropping moth (Ponometia candefacta) larvae feed on the foliage.

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

2, 3, 4, 5, 7, 28, 29, 30.

 
  3/30/2023      
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

 

 
         
 
Taxonomy
 
  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (flowering plants)  
  Superorder Asteranae  
 

Order

Asterales (sunflowers, bellflowers, fanflowers, and allies)  
 

Family

Asteraceae (sunflowers, daisies, asters, and allies)  
  Subfamily Asteroideae  
  Supertribe Helianthodae  
  Tribe Heliantheae (sunflowers and allies)  
  Subtribe Ambrosiinae (cockleburs, ragweeds, and wild quinines)  
  Genus Ambrosia (ragweeds)  
       
 

Subordinate Taxa

 
 

 

 
       
 

Synonyms

 
 

Ambrosia californica

Ambrosia coronopifolia

Ambrosia cumanensis

Ambrosia psilostachya var. californica

Ambrosia psilostachya var. coronopifolia

Ambrosia psilostachya var. lindheimeriana

Ambrosia rugelii

 
       
 

Common Names

 
 

cuman ragweed

naked-spiked ragweed

perennial ragweed

western ragweed

 

 

 

 

 

 

 

 

 

 

Glossary

Achene

A dry, one-chambered, single-seeded fruit, formed from a single carpel, with the seed attached to the membranous outer layer (wall) only by the seed stalk; the wall, formed entirely from the wall of the superior ovary, does not split open at maturity, but relies on decay or predation to release the contents.

 

Allelopathy

The release of a chemical toxin by one plant to inhibit the growth or germination of nearby competing plants.

 

Axil

The upper angle where the leaf stalk meets the stem.

 

Bipinnatifid

Twice pinnatifid. Cut deeply into lobes with each lobe also cut into deep lobes.

 

Palmately Lobed

Similar to a hand. Having more than three lobes that radiate from a single point at the base of the leaf.

 

Pinnatifid

Deeply cut, more than half way to the midrib but not to the midrib, into lobes that are spaced out along the midrib; the lobes do not form separate leaflets.

 

Rhizome

A horizontal, usually underground stem. It serves as a reproductive structure, producing roots below and shoots above at the nodes.

 
 
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Plant

 
    western ragweed   western ragweed  
           
 

Inflorescence

 
    western ragweed   western ragweed  
           
 

Leaves

 
    western ragweed   western ragweed  

 

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Other Videos
 
  WESTERN RAGWEED
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About

Uploaded on Aug 23, 2011

A sunflower member with a small heat of disk florets. Common along roads.

   

 

Camcorder

 
 
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