Annuals, 30–200(–300) cm, sweetly aromatic. Stems mostly 1, erect, green, turning to reddish brown with age, simple (smooth or ribbed), glabrous or sparsely hairy. Leaves cauline, bright green; blades triangular to broadly ovate, 2–5(–10) × 2–4 cm, 2–3-pinnatifid (lobes relatively narrow, ± toothed), faces glabrous, gland-dotted. Heads (nodding, peduncles 2–5 mm) in open, (diffusely branched, leafy) arrays 15–30(–40) × 10–20 cm. Involucres globose, 1.5–2.5 × 1.5–2.5 mm. Phyllaries (green) lanceolate, glabrous. Florets: pistillate (0–)10–20; bisexual 18–24; corollas pale yellow (broadly campanulate), 0.5–1 mm, glabrous. Cypselae oblong (flattened), 0.3–0.8 mm, glabrous. 2n = 18.
Phenology: Flowering late summer–fall.
Habitat: Moist waste areas, sandy soils
Elevation: 0–2000 m
Introduced; N.B., Ont., Que., Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Miss., Mont., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., Tenn., Tex., Vt., Va., Wash., W.Va., Wis., Wyo., Eurasia.
Widely cultivated for aromatic oils, Artemisia annua often persists in gardens, becoming naturalized in moist-temperate areas (especially in eastern United States). Reports of naturalization may be exaggerated (reported for Prince Edward Island, but not established).
The systematic placement of this species appears to align most closely with species of the Eurasian subg. Seriphidium (L. E. Watson et al. 2002). Molecular evidence suggests that the Artemisia annua lineage may be ancestral to woody species in the Old World.