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annual ragweed, common ragweed, petite herbe à poux

bur ragweed, lagoonweed, woolly-leaf bur ragweed, woollyleaf burr ragweed, woollyleaf bursage, woollyleaf franseria, woollyleaf povertyweed

Habit Annuals, 10–60(–150+) cm. Perennials, 10–30+ 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 10–45+ mm;

blades elliptic to ovate, 45–60(–100+) × 30–45(–75+) mm, usually 1–2-pinnately lobed (lobes ± lanceolate), bases cuneate, ultimate margins serrate, abaxial faces densely sericeous or strigillose (silver or grayish), adaxial faces strigillose.

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 1–2 mm;

involucres saucer-shaped, 3.5–5+ mm diam., strigillose;

florets 8–25(–40+).

Pistillate heads

clustered, proximal to staminates;

florets 1.

clustered, proximal to staminates;

florets (1–)2.

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 ± pyriform to globose, 3–5+ mm, stipitate-glandular, spines 8–12+, scattered, stoutly conic, 0.5–1+ mm, tips straight.

2n

= 34, 36.

= 36.

Ambrosia artemisiifolia

Ambrosia grayi

Phenology Flowering Jul–Oct. Flowering Aug–Sep.
Habitat Wet to dry soils, disturbed sites Wet or seasonally wet flats, depressions, alkaline, clay soils, prairies
Elevation 0–1000+ m (0–3300+ ft) 600–1200 m (2000–3900 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
[WildflowerSearch map]
[BONAP county map]
from FNA
CO; KS; NE; OK; TX
[WildflowerSearch map]
[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. FNA vol. 21, p. 17.
Parent taxa Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Ambrosia 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
A. acanthicarpa, A. ambrosioides, A. artemisiifolia, A. bidentata, A. chamissonis, A. cheiranthifolia, A. chenopodiifolia, A. confertiflora, A. cordifolia, A. deltoidea, A. dumosa, A. eriocentra, 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 Gaertneria grayi
Name authority Linnaeus: Sp. Pl. 2: 988. (1753) (A. Nelson) Shinners: Field & Lab. 17: 174. (1949)
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