11.
Ambrosia bidentata
Michaux, Fl. Bor.-Amer. 2: 182. 1803.
Annuals,
10—30(—100+) cm.
Stems
erect.
Leaves
mostly opposite; petioles 0—0.5 mm; blades ± lanceolate to lance-linear, 15—40+ × 3—6(—10+) mm, bases rounded to cordate, margins entire or with (1—)2(—4) basal lobes, abaxial and adaxial faces ± piloso-hispid and gland-dotted.
Pistillate heads
clustered, proximal to staminates; florets 1.
Staminate heads:
peduncles 0—0.5 mm; involucres obliquely cup-shaped (lateral lobe longer than others), 2.5—4 mm diam., piloso-hispid; florets 6—8+.
Burs:
bodies pyramidal, 5—8 mm, piloso-hispid, spines 4(—5), ± distal, ± acerose, 0.5—1 mm, tips straight.
Flowering Jul—Oct. Dry, disturbed sites; 200—500 m; Ala., Ark., Conn., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Minn., Miss., Mo., N.C., Ohio, Okla., Tenn., Tex., Va., W.Va.
Hybrids between
Ambrosia bidentata
and
A. trifida
have been recorded.
