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Ambrosia artemisiifolia
Ambrosia artemisiifolia
L.
Family:
Asteraceae
annual ragweed,
more...
common ragweed, low ragweed, ragweed, Roman wormwood, short ragweed, small ragweed (es: estafiate, artemisia)
Max Licher
Flora of North America
General Description
Resources
John L. Strother in Flora of North America (vol. 21)
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.
Pistillate heads
clustered, proximal to staminates; florets 1.
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+.
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.
2
n
= 34, 36. Flowering Jul-Oct. Wet to dry soils, disturbed sites; 0-1000+ m; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo. 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
.
Plant
: Annual < 7 dm, much-branched; Stem green, red- or black-marked, weakly hairy
Leaves
: opposite below; cauline leaves 3-12 cm, widely ovate, generally 2-3-pinnately parted, ± hairy
INFLORESCENCE
: primary inflorescence a head, each resembling a flower; staminate heads generally many in ± spikes or racemes, 2-5 mm diam, involucre asymmetric, lobes 5-10, green; pistillate heads 1-flowered, generally spiny, bur-like; receptacle chaffy; chaff scales spirally arrayed, fused below, tips generally becoming spiny
Flowers
: Staminate flowers ± many; corolla yellow or translucent; anthers free; style unbranched; Pistillate flowers 1-5; corolla 0; style branches long
Fruit
: Fruit: enclosed in bur 2-4 mm, widely obconic, green to brown, ± puberulent; spines 4-12, blunt, vestigial, ± in 1 whorl below beak; pappus 0
Misc
: Disturbed sites; < 650 m.; Aug-Oct
Open Interactive Map
Max Licher
Tony Frates
Tony Frates
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