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heartleaf bursage, Tucson bur ragweed, Tucson burr ragweed

annual ragweed, common ragweed, petite herbe à poux

Habit Shrubs, 30–50+ cm. Annuals, 10–60(–150+) cm.
Stems

erect.

erect.

Leaves

mostly alternate;

petioles 3–35 mm;

blades deltate to rounded-deltate, 10–35(–80) × 10–30(–70) mm, bases cordate to truncate, margins coarsely toothed, abaxial faces densely puberulent (including veins), adaxial faces strigillose to scabrellous and gland-dotted.

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 0–1 mm;

involucres cup-shaped, 2–3(–5) mm diam., strigillose;

florets 8–30+.

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–)2.

clustered, proximal to staminates;

florets 1.

Burs

bodies ± globose to fusiform, 3–4+ mm, tomentulose and stipitate-glandular, spines 8–20+, scattered, ± subulate (basally navicular), 1–2 mm, tips straight or uncinate.

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 cordifolia

Ambrosia artemisiifolia

Phenology Flowering Mar–Apr. Flowering Jul–Oct.
Habitat Sandy washes, benches Wet to dry soils, disturbed sites
Elevation 700–1200 m (2300–3900 ft) 0–1000+ m (0–3300+ ft)
Distribution
from FNA
AZ; Mexico (Sinaloa, Sonora)
[WildflowerSearch map]
[BONAP county map]
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]
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. 14. FNA vol. 21, p. 15.
Parent taxa Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Ambrosia Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Ambrosia
Sibling taxa
A. acanthicarpa, A. ambrosioides, A. artemisiifolia, A. bidentata, A. chamissonis, A. cheiranthifolia, A. chenopodiifolia, A. confertiflora, 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. 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 Franseria cordifolia A. artemisiifolia var. elatior, A. artemisiifolia var. paniculata, A. elatior, A. glandulosa, A. monophylla
Name authority (A. Gray) W. W. Payne: J. Arnold Arbor. 45: 421. (1964) Linnaeus: Sp. Pl. 2: 988. (1753)
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