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beach bur-sage

giant ragweed

Habit Plants perennial, 5–40 dm, mat-forming; taprooted or from root crowns.
Stems

prostrate or decumbent; simple to much branched; ± densely pilose to villous or strigose.

Leaves

alternate;

blades lanceolate, broadly elliptic, obovate, or triangular;

surfaces strigose-canescent, petiolate.

Involucres

cup-shaped.

Pistillate florets

1.

Staminate florets

8–30+.

Phyllaries

of staminate heads connate, sometimes with black midribs;

tips shallowly lobed;

surfaces glabrous or strigose; of pistillate heads erect, separate, marginally glabrous or pilose.

Burs

ovoid, 5–10 mm, variously pubescent;

spines flattened, spreading or arched outward, 0.5–2 mm.

2n

=36.

Ambrosia chamissonis

Ambrosia trifida

Distribution
[WildflowerSearch map]
[BONAP county map]
[WildflowerSearch map]
[BONAP county map]
Discussion

Western North America. 2 varieties.

Source Flora of Oregon, volume 2, page 172
Kenton Chambers
Sibling taxa
A. acanthicarpa, A. artemisiifolia, A. grayi, A. psilostachya, A. trifida
A. acanthicarpa, A. artemisiifolia, A. chamissonis, A. grayi, A. psilostachya
Subordinate taxa
A. chamissonis var. bipinnatisecta, A. chamissonis var. chamissonis
Synonyms Franseria chamissonis Ambrosia trifida var. trifida
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