Scientific Family
Asteraceae
Synonyms
Ambrosia californica, Ambrosia coronopifolia, Ambrosia cumanensis
Other common names
perennial ragweed
Plant type
Forbs and Subshrubs
Origin
Native
Lifecycle
Annual or perennial
Height
To 3 feet
Riparian
Yes
The plants are erect with a slender, branching, straw-colored stem rising from rhizome-like roots. Plants are monoecious with unisexual flowers. Western ragweed is one of the main hay-fever plants in late summer when it is in bloom.
Perennial rhizomatous herb. Leaves opposite and alternate, pinnatifid with broad midstripe, rough-hairy and glandular. Staminate heads pendant in terminal racemes; pistillate heads in upper leaf axils or in racemes below staminate heads.
Habitat
Roadsides, disturbed places and along streams, often wet, alkaline, clay soils.
Plant Community
Riparian
Disturbed Areas
Low elevation
850
High elevation
7400
Flower Characteristics
The male flower heads are numerous and contain 5 to 10 tiny yellow flowers. They occur at the top of the plant in elongated clusters arising from the upper leaf axils. Female flower heads are green, inconspicuous and are borne below in the leaf axils.
Flower color
Green, yellow
Flower shape
Bell-shaped
Tubular
No
First bloom month
July
Last bloom month
October
Flower clusters
Elongated
Leaf and Stem Characteristics
The erect stems are slender and branched. Leaves are pinnately lobed. Lobes are entire or toothed. Lower leaves are opposite, upper leaves are alternate.
Leaf type
Simple
Leaf color
Green
Leaf shape
Pinnatifid
Leaf margin
Toothed
Leaves clasp
No
Leaf hairs
Leaves & stems
Spines
No
Fruit and Seed Characteristics
Fruit type
Achene
Fruit color
Greenish-brown
Short beaked bur, 1/8 to 1/4 inch long, with a few rounded projections.