13.
Ambrosia artemisiifolia
Linnaeus, Sp. Pl. 2: 988. 1753.
Petite herbe à poux
Ambrosia artemisiifolia
var.
elatior
(Linnaeus) Descourtilz;
A.
artemisiifolia
var.
paniculata
(Michaux) Blankinship;
A. elatior
Linnaeus;
A. glandulosa
Scheele;
A.
monophylla
(Walter) Rydberg
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
.
