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annual ragweed, common ragweed, petite herbe à poux

Habit Annuals, 10–60(–150+) cm.
Stems

erect.

Leaves

opposite (proximal) and alternate;

petioles 25–35(–60+) mm;

blades deltate to lanceolate or elliptic, 25–55(–90+) × 20–30(–50+) mm, 1–2-pinnately lobed, bases cuneate, ultimate margins entire or toothed, abaxial faces sparsely pilosulous to strigillose, adaxial faces strigillose, both gland-dotted.

Staminate heads

peduncles 0.5–1.5 mm;

involucres shallowly cup-shaped (usually without black nerves), 2–3+ mm diam., glabrous or hispid to pilosulous;

florets 12–20+.

Pistillate heads

clustered, proximal to staminates;

florets 1.

Burs

bodies ± globose to pyriform, 2–3 mm, ± pilosulous, spines or tubercles 3–5+, near middles or distal, ± conic to acerose, 0.1–0.5+ mm, tips straight.

2n

= 34, 36.

Ambrosia artemisiifolia

Phenology Flowering Jul–Oct.
Habitat Wet to dry soils, disturbed sites
Elevation 0–1000+ m (0–3300+ ft)
Distribution
from FNA
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK
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[BONAP county map]
Discussion

Hybrids between Ambrosia artemisiifolia and A. psilostachya have been called A. ×intergradiens W. H. Wagner. The name Ambrosia ×helenae Rouleau applies to hybrids between A. artemisiifolia and A. trifida.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 21, p. 15.
Parent taxa Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Ambrosia
Sibling taxa
A. acanthicarpa, A. ambrosioides, A. bidentata, A. chamissonis, A. cheiranthifolia, A. chenopodiifolia, A. confertiflora, A. cordifolia, A. deltoidea, A. dumosa, A. eriocentra, A. grayi, A. hispida, A. ilicifolia, A. linearis, A. monogyra, A. psilostachya, A. pumila, A. salsola, A. tomentosa, A. trifida
Synonyms A. artemisiifolia var. elatior, A. artemisiifolia var. paniculata, A. elatior, A. glandulosa, A. monophylla
Name authority Linnaeus: Sp. Pl. 2: 988. (1753)
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