western ragweed

(Ambrosia psilostachya)

               
Conservation Status

IUCN Red List

not yet assessed

western ragweed

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

Nativity

Native

Occurrence

 

Habitat

Dry. Prairies, disturbed sites.

Flowering

August to September

     
Flower Color

Green

     
Height

12 to 40, usually 12 to 24

     

Identification

This 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.

 
Similar
Species

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

Giant ragweed (Ambrosia trifida var. 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.


Distribution Distribution Map   Sources: 2, 3, 4, 5, 7, 28.

Comments

 


Taxonomy

Family:

Asteraceae (aster)

 

Subfamily:

Asteroideae

 

Supertribe:

Helianthodae

 

Tribe:

Heliantheae (sunflower)

 

Subtribe:

Ambrosiinae

 
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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  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.

 
     

 

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