Ambrosia artemisiifolia |
Ambrosia chenopodiifolia |
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annual ragweed, common ragweed, petite herbe à poux |
San Diego bur ragweed, San Diego bur-sage, San Diego burr ragweed |
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Habit | Annuals, 10–60(–150+) cm. | Shrubs, 30–80+ cm. |
Stems | erect. |
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. |
mostly alternate; petioles 5–20 mm; blades ovate to rounded-deltate, 20–35(–50) × 18–30(–45) mm, bases broadly cuneate to ± truncate, margins toothed, abaxial faces ± densely tomentulose (between veins), adaxial faces sparsely tomentulose, glabrescent. |
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+. |
peduncles 0–3 mm; involucres ± cup-shaped, 3–5 mm diam., tomentulose; florets 12–20+. |
Pistillate heads | clustered, proximal to staminates; florets 1. |
clustered, proximal to staminates; florets 2(–3). |
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. |
bodies obconic to fusiform, 4–6 mm, tomentulose (little, if at all, stipitate-glandular), spines 15–20+, scattered or on distal 1/2, ± subulate (the proximal basally flattened), 2–3 mm, tips usually uncinate, sometimes straight. |
2n | = 34, 36. |
= 72. |
Ambrosia artemisiifolia |
Ambrosia chenopodiifolia |
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Phenology | Flowering Jul–Oct. | Flowering Mar–Apr. |
Habitat | Wet to dry soils, disturbed sites | Clays or sandy soils, among lava rocks |
Elevation | 0–1000+ m (0–3300+ ft) | 50–200 m (200–700 ft) |
Distribution |
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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CA; Mexico (Baja California, Baja California Sur)
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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.) |
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Source | FNA vol. 21, p. 15. | FNA vol. 21, p. 14. |
Parent taxa | Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Ambrosia | Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Ambrosia |
Sibling taxa | ||
Synonyms | A. artemisiifolia var. elatior, A. artemisiifolia var. paniculata, A. elatior, A. glandulosa, A. monophylla | Franseria chenopodiifolia |
Name authority | Linnaeus: Sp. Pl. 2: 988. (1753) | (Bentham) W. W. Payne: J. Arnold Arbor. 45: 419. (1964) |
Web links |
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