Biorepository Data Portal

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.

Branching annual weed 3-10 dm, the stem conspicuously spreading-hirsute, especially above; lvs numerous, sessile, opposite below, alternate above, lanceolate, acuminate, 2.5-7 cm נ4-10 mm, usually with a single pair of sharp large teeth below the middle, hirsute to scabrous, or the upper side glabrous; staminate heads sessile, the invol strongly oblique, its upper side produced into a conspicuous, retrorsely spreading, hispid-hirsute, lanceolate to triangular- ovate lobe, the bractless infl thus appearing retrorse-bracteate; fruiting invol 5-8 mm, villous-hirsute, several-ribbed, the ribs produced into short, stiff spines; 2n=34. Prairies and waste places; O. and Ky. to Nebr., La., and Tex., and occasionally intr. elsewhere. July-Oct.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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