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Erect, glabrous, strongly aromatic annual, up to 1-2 m tall. Stems usually with many short branches. Lvs 1-pinnate, shortly petiolate; leaflets in 3-8 pairs, linear to lanceolate, 2-8 cm long, with (8)-15-40 teeth on each side, moderately covered in large, sessile, glands, especially on lower surface. Upper cauline lvs smaller than lower, with fewer leaflets and teeth. Capitula 3-7 mm diam., in dense corymbs; peduncles solid. Involucre narrow-cylindric, 8-12 × 2-3 mm, with 3-5 short teeth at apex; glands long, many, evenly distributed above and below. Ray florets 1-3-(4); ligules yellowish green or cream, 1-3 mm long. Disc florets few, green. Achenes 3-4-angled toward base, dark brown, densely clothed in short antrorse hairs, 5.5-7 × 0.7-1 mm; pappus scales free, the longest 2.5-3 mm and with minute marginal antrorse hairs.
Annual herb, 10-250 cm high; whole plant aromatic; stems much branched in larger plants, almost woody in larger plants, ribbed, glabrous, glandular. Leaves mostly opposite but often alternate in upper part of plant, dark green, pinnatisect, elliptic in outline, 3-30 cm long, 0.7-8 cm wide, the rachis thinly winged, lobes up to 17, linear-oblong, to 11 cm long and 1 cm wide, with orange glands. Capitula many in dense terminal corymbs, narrowly cylindric; involucre 8-12 mm long; phyllaries 3-4, yellow-green, fused, glabrous, with brown or orange linear glands. Ray florets 2-3, pale yellow to cream, the ray 2-3.5 mm long; disc florets 4-7, yellow to dark yellow, 4-5 mm long. Achenes black, narrowly ellipsoid, 6-7 mm long, pilose; pappus of 1-2 setae to 3 mm long and 3-4 scales to 1 mm long, these with ciliate apex.
Annual herb, up to 3 m high; erect, glabrous, strongly aromatic. Stems simple or diffusely branched. Leaves opposite or alternate, sessile, pinnate, lobes lanceolate, margins sharply serrate. Capitula radiate, few-flowered, solitary on long peduncles or corymbosely arranged; involucre cylindric; bracts in 1 row. Receptacle flat, epaleate. Ray florets female, fertile; corolla pale to lemon-yellow, strap-shaped. Style branches linear-lanceolate. Disc florets bisexual, fertile; corolla yellow, tubular, expanded above, 5-fid. Anthers with obtuse base, apical appendage lanceolate. Style branches narrowly oblong, truncate and penicillate, papillose on outer faces. Flowering time Oct.-Apr. Pappus of few scales, sometimes awned. Cypselae linear, narrowed to base, compressed or angled.
Annual herbs, 10-250 cm, plant aromatic. Stems much branched in larger plants and almost woody, ribbed, glabrous, glandular. Leaves mostly opposite, often alternate in upper part, dark green, pinnatisect, elliptic in outline, 3-30 × 0.7-8 cm, rachis narrowly winged, lobes up to 17, linear-oblong, to 11 × 1 cm, with orange glands. Synflorescence a dense terminal corymb. Capitula narrowly cylindric; involucre 8-12 mm; phyllaries 3 or 4, yellow-green, fused, glabrous, with brown or orange linear glands. Ray florets 2 or 3, pale yellow to cream, lamina 2-3.5 mm. Disk florets 4-7, yellow to dark yellow, 4-5 mm. Achenes black, narrowly ellipsoid, 6-7 mm, pilose; pappus of 1 or 2 setae to 3 mm and 3 or 4 scales to 1 mm, apices ciliate.
Slender annual herb to 200 cm high. Stems glabrous, striate. Leaves opposite on lower parts of plant, alternate above, pinnately divided with 5–11 segments, glabrous; segments narrowly lanceolate, 1.2–6 cm long, 0.2–0.8 cm wide, serrate, acute, with 10–30 submarginal elliptic oil glands. Capitula numerous, in dense corymbose cymes; peduncles 2–6 mm long; involucre cylindrical, 1.7–3.5 mm diam. at anthesis; involucral bracts 3 (or 4), connate except near apex, 8–12 mm long, obtuse. Ray florets 1–3; ligule pale yellow to cream. Disc florets 4–7; corolla 2–4 mm long, with antrorse eglandular hairs. Achenes linear, 6–8.5 mm long, black, faintly striate. Pappus of 4–6 acute translucent scales, the longest 2.8–3.5 mm long.
Annual herb, up to 3 m high; all parts with embedded oil sacs, aromatic. Leaves opposite or alternate in upper part, petiolate; blade pinnately dissected, leaflets narrowly ovate, margins sharply serrate, base half-clasping. Heads minutely radiate, many in congested, terminal, corymbose panicles. Involucre narrowly cylindric; bracts uniseriate, connate nearly to top, with embedded oil sacs. Flowers: ray and disc florets creamy white; Feb.-May. Fruit with cypsela awl-shaped, black. Pappus of several scales, one much elongated.
Annuals, 30–100(–180+) cm. Leaf blades 80–150+ mm overall, lobes or leaflets 9–17+, narrowly lanceolate to lance-linear, 12–25(–50+) × (2–)4–7+ mm. Heads in ± corymbiform clusters. Peduncles 1–5+ mm. Involucres 7–10+ × 1.5–3 mm. Ray florets 1–3; laminae yellow, ± ovate to elliptic, 1–2 mm. Disc florets 3–5; corollas 3–4 mm. Cypselae (4.5–)6–7+ mm; pappi of 1–2 ± subulate scales 2–3+ mm plus 3–5 distinct, ovate to lanceolate scales 0.5–1 mm. 2n = 48.
Strong-smelling annual 3–10 dm; lvs pinnately compound; lfls 9–17, lance-linear, 1.5–6 cm, sharply serrate; heads numerous, tending to form flat-topped clusters; invol narrowly cylindric, 8–12 mm, with 3–5 short teeth, few-fld, the rays commonly 3, only 1–2 mm; achenes 5–6 mm; longer pappus-scales 2–3 mm, the others less than 1 mm; 2n=48. Native of S. Amer., now ± established as a weed in disturbed sites n. to Va. and rarely beyond. Aug.–Oct.
An annual herb. It grows 1-2 m high. The stems are ribbed. The leaves are compound and alternate or opposite. They are 10-12 cm long with 3-9 leaflets. The leaflets are 1-8 cm long by 5-9 mm wide. The flowers occur in a panicle of heads at the end of the branches or in the axils of leaves. The flower heads are 2-5 mm across. They are white and yellow in the centre. The fruit is a black nut. It is 5-8 mm long. It is hairy.
Annual herb, up to 3 m high; all parts with embedded oil sacs. Leaves pinnately dissected, leaflets lanceolate, margins sharply serrate. Heads many in congested terminal corymbose panicles. Pappus of several scales, 1 much elongated. Flowers creamy white.
