Ambrosia artemisiifolia

Species category

Weed

Common name

annual ragweed

Diagnostic characters

Planting unit

AcheneAchene:
A dry, hard, one-chambered, one-seeded indehiscent fruit, as in buckwheat (Fagopyrum) or sunflower (Helianthus). The fruit wall is not united with the seed coat.
in an involucreInvolucre:
A number of bracts (often leaf-like) that subtend an inflorescence such as the head in sunflowers.

Shape

ObovateObovate:
Inverted egg shaped with apical end the broadest.

Size

Length: 3 mm
Width: 2 mm
Thickness: 2 mm

Color

Brown

Texture

Smooth apicalApical:
The distal end of the fruit or seed away from the point of attachment or attachment scar.
points

Other structures

StylarStylar:
The end of the fruit or seed that contains the style or the apical end.
and shoulder points.

Identification notes

Seed type is best described as an acheneAchene:
A dry, hard, one-chambered, one-seeded indehiscent fruit, as in buckwheat (Fagopyrum) or sunflower (Helianthus). The fruit wall is not united with the seed coat.
enclosed in an involucreInvolucre:
A number of bracts (often leaf-like) that subtend an inflorescence such as the head in sunflowers.
. SpikesSpike:
Has a strong central axis (rachis) on which flowers or spikelets are directly attached (sessile), e.g. wheatgrasses.
on apicalApical:
The distal end of the fruit or seed away from the point of attachment or attachment scar.
end represent tips of involucreInvolucre:
A number of bracts (often leaf-like) that subtend an inflorescence such as the head in sunflowers.
bracts. Ambrosia trifida is substantially larger than the other two. A. artemisifolia has a smaller and more pointed base than A. psilostachya. A. psilostachya is more hairy.

Comments

See first photo for more details.

Noxious weed seed categories

State Noxious Weed: Oregon, Hawaii

AOSA examination list

Included

More information

For more information, see ISMA fact sheet.

Nomenclature

Family

Asteraceae

Valid name

Ambrosia artemisiifolia L.

From Left to Right: 1. Ambrosia trifida 2. Ambrosia artemisifolia upper central figure achene (fruit) upper right: cross-section showing outside layers of the head, achene, and seed.	Ambrosia artemisiifolia. The Ambrosia "seed" is equivalent to a "head" in the Asteraceae family. The spikes are the ends of the involucre bracts subtending the head. The seed is then a combination of the involucre, the pericarp, and the true seed. It may be described as an achene in an involucre.
From Left to Right: 1. Ambrosia artemisiifolia 2. Ambrosia psilostachya 3. Ambrosia trifida.	Ambrosia artemisiifolia. Multiple views of fruit. Burs (=disseminules). Photo by Michael K. Kirkpatrick, USDA-APHIS-PPQ.