Ambrosia artemisiifolia |
Ambrosia eriocentra |
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annual ragweed, common ragweed, petite herbe à poux |
woolly bur-sage, woolly fruit bur ragweed, woollyfruit burr ragweed |
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Habit | Annuals, 10–60(–150+) cm. | Shrubs, 30–80(–120+) 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 0–2 mm; blades (± white abaxially) elliptic, lance-linear, or rhombic, 10–40(–60) × 5–15(–40) mm, bases ± cuneate, margins irregularly toothed to ± laciniate, abaxial faces densely strigillose, adaxial faces tomentulose and pilosulous. |
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 0–0.5 mm; involucres saucer-shaped to shallowly cup-shaped, 4–8+ mm diam., tomentulose and/or pilose; florets 12–25+. |
Pistillate heads | clustered, proximal to staminates; florets 1. |
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. |
bodies obconic to fusiform, 3–5+ mm, densely villous and stipitate-glandular, spines 12–20+, scattered or mostly distal, ± subulate, 3–4 mm, tips straight. |
2n | = 34, 36. |
= 36. |
Ambrosia artemisiifolia |
Ambrosia eriocentra |
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Phenology | Flowering Jul–Oct. | Flowering Apr–May(–Jul). |
Habitat | Wet to dry soils, disturbed sites | Sandy and gravelly washes |
Elevation | 0–1000+ m (0–3300+ ft) | 700–1700 m (2300–5600 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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AZ; CA; NV; UT
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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. 13. |
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 eriocentra |
Name authority | Linnaeus: Sp. Pl. 2: 988. (1753) | (A. Gray) W. W. Payne: J. Arnold Arbor. 45: 423. (1964) |
Web links |
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