western ragweed

(Ambrosia psilostachya)

Conservation Status
western ragweed
  IUCN Red List

not listed


N4N5 - Apparently Secure to Secure

SNR - Unranked


not listed

Wetland Indicator Status
  Great Plains

FACU - Facultative upland


FACU - Facultative upland

  Northcentral & Northeast

FAC - Facultative


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.




12 to 40, usually 12 to 24


Flower Color




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.


Dry. Prairies, disturbed sites.




August to September


Pests and Diseases


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




Distribution Map



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









  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  


Asterales (sunflowers, bellflowers, fanflowers, and allies)  


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






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













A dry, one-chambered, single-seeded seed capsule, 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.



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



The upper angle where the leaf stalk meets the stem.



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.



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.



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

Visitor Photos

Share your photo of this plant.

  This button not working for you?
Simply email us at info@MinnesotaSeasons.com.
Attach one or more photos and, if you like, a caption.




MinnesotaSeasons.com Photos


    western ragweed   western ragweed  


    western ragweed   western ragweed  


    western ragweed   western ragweed  






Visitor Videos

Share your video of this plant.

  This button not working for you?
Simply email us at info@MinnesotaSeasons.com.
Attach a video, a YouTube link, or a cloud storage link.


Other Videos

Uploaded on Aug 23, 2011

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




Visitor Sightings

Report a sighting of this plant.

  This button not working for you?
Simply email us at info@MinnesotaSeasons.com.
Be sure to include a location.


MinnesotaSeasons.com Sightings

Agassiz Dunes SNA (MN DNR)

Anna Gronseth Prairie

Antelope Valley SNA

Badoura Jack Pine Woodland SNA

Big Stone Lake State Park

Blanket Flower Prairie SNA

Blazing Star Prairie Addition Preserve, South Unit

Blue Devil Valley SNA

Blue Mounds State Park

Buffalo River State Park

Bunker Hills Regional Park

Bur Oak WMA

Cedar Mountain SNA

Chippewa Prairie

Cottonwood River Prairie SNA

Crow Wing State Park

Des Moines River SNA

Dodge Nature Center

Felton Prairie SNA, Bicentennial Unit

Foxhome Prairie

Frenchman’s Bluff SNA

Glendalough State Park

Gneiss Outcrops SNA

Grey Cloud Dunes SNA

Hastings Sand Coulee SNA

Helen Allison Savanna SNA

Hole-in-the-Mountain Prairie

Holthe Prairie SNA

Kasota Prairie SNA

Kellogg Weaver Dunes SNA, Kellogg Weaver Unit

Kettledrummer Prairie

Leif Mountain

Margherita Preserve-Audubon Prairie

Mille Lacs Kathio State Park

Minneopa State Park

Mound Prairie SNA

Mound Spring Prairie SNA, North Unit

Mound Spring Prairie SNA, South Unit

Neal WMA

Northern Tallgrass Prairie NWR, Hoffman Unit

Northern Tallgrass Prairie NWR, Pavia Unit

Northern Tallgrass Prairie NWR, Rengstorf Unit

Northern Tallgrass Prairie NWR, Spieker Unit

Old Mill State Park

Ordway Prairie

Otter Tail Prairie SNA

Pankratz Memorial Prairie, North Unit

Pembina Trail Preserve SNA, Pembina Trail Unit

Phelps Lake WMA

Plover Prairie, East Unit

Prairie Creek WMA, Koester Prairie Unit

Red Rock Prairie

Rice Lake Savanna SNA

Richard M. & Mathilde Rice Elliott SNA

River Terrace Prairie SNA

Rock Ridge Prairie SNA

Rushford Sand Barrens SNA

St. Croix Savanna SNA

Sand Prairie Wildlife Management and Environmental Education Area

Sandpiper Prairie SNA

Sedan Brook SNA

Sheepberry Fen

Shooting Star Prairie SNA

Spring Prairie Preserve

Springbrook Nature Center

Strandness Prairie

Swedes Forest SNA

Town Hall Prairie

Twin Lakes SNA

Twin Valley Prairie Addition

Uncas Dunes SNA

Upper Sioux Agency State Park

Western Prairie SNA

Whitetail Woods Regional Park

Wild River State Park

William O’Brien State Park

Yellow Bank Hills SNA

Zimmerman Prairie







Last Updated:

© MinnesotaSeasons.com. All rights reserved.

About Us

Privacy Policy

Contact Us