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Yavapai County Native & Naturalized Plants

Ambrosia acanthicarpa - flatspine bur ragweed

Plant Form: Forb or Subshrub

Family: Asteraceae

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Max Licher @
Max Licher @
Young plant - leaves
Max Licher @
Forb Plant Description

Origin: Native   Life Cycle: Annual
General Desc: This spiny, weedy plant grows in clumps of many erect stems.
Identification notes: The involucres (whorl of bracts) of staminate heads (flowers have stamens but not pistels) usually each with 1 to 5+ black nerves. The fruit burs are spindle to inversely pyramidal in shape. Leaf blades are mostly 1 to 2 pinnately lobed.
Height: 2 to 3 feet


Habitat Description: It is adaptable and grows well in disturbed areas, easily becoming weedy.
Plant Communities: Desert Scrub, Interior Chaparral, Semidesert Grasslands, Pinyon Juniper Woodland, Montane Conifer Forest, Riparian, Disturbed Areas
Elevation: 50 - 9800 feet

Flower Characteristics

Color: Greenish to yellow     Shape: Daisy or dandelion-like in elongated clusters     Tubular: N     Flowering Period: Jul - Nov
Description: Flower head appears to be a single flower, but is composed of several flowers (a composite). The corolla is lacking. There are many tiny greenish flowers on the stem facing downward. Male flowers are separate and above the female flowers.

Leaf and Stem Characteristics

Leaf Color: Grayish-green     Leaf Type: Simple     Leaf Shape: Pinnatifid     Leaf Margin: Lobed     Leaf Attachment: Alternate and opposite     Leaves Clasp: N
Hairs: Leaves and stems     Spines: N
Leaf Description: Opposite below, alternate above; simple; lobed bipinnatifid to pinnatifid; blades 1/3 inch to 3-3/4 inches long, 1/4 to 3 inches wide.

Fruit and Seed Characteristics

Fruit Color: Purplish   
Fruit Type: Achene
Fruit Notes: 1 seeded with hard shell covered with curved spines.

  Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr #C
Prescott, AZ 86305
(928) 445-6590
Version 8.0  
Last Updated: Nov 21, 2021
Content Questions/Comments: Email Mary Barnes  
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