Annuals [perennials], (10-)50-100[-250] cm. Leaves: petioles 20-40 mm; blades deltate or lanceolate to lance-linear overall, (30-)50-120(-220) × 10-50(-150) mm, sometimes either 1-pinnately lobed, primary lobes 3-5+, lanceolate to lance-linear, 30-120 × 3-25+ mm, or 2-pinnatisect, ultimate lobes linear, 5-30 × 1-2+ mm, bases truncate to cuneate, ultimate margins entire or serrate, seldom ciliate, apices obtuse to acuminate, faces glabrous or puberulent. Heads in ± corymbiform arrays. Peduncles (10-)40-60+ mm. Calyculi of 8-12(-17) usually erect, linear, seldom foliaceous bractlets 3-6 mm, margins ciliate, abaxial faces usually glabrous, sometimes hispidulous at bases. Involucres campanulate to hemispheric, 4-6 × 5-10 mm. Phyllaries 8-12, ovate to lanceolate, 4-5(-7) mm (margins usually yellow). Ray florets 5-6; laminae yellow, 10-30 mm. Disc florets 12-30(-60+); corollas yellowish, 3-4 mm. Cypselae dark brown to blackish, ± flattened, sometimes unequally 3-4-angled, ± linear, outer 4-6 mm, inner 5-7 mm, margins not barbed or ciliate, apices truncate, faces weakly 2-grooved, glabrous or sparsely strigillose, sometimes tuberculate; pappi 0, or of (1-)2(-4) erect to spreading, retrorsely barbed awns (1-)1.5-4 mm. 2n = 24 (Mexico).

Flowering mostly Aug-Sep. Marshes, borders of streams, other wet sites; 900-2000 m; Ariz.; Mexico; Central America; introduced in Europe.

Duration: Perennial

Nativity: Native

Lifeform: Forb/Herb

General: Perennial herb, 50-100 cm tall; stems erect, 4-angled, simply branched; herbage glabrous, rarely pubescent on young plants.

Leaves: Opposite and petiolate, the petioles 2-4 cm long; blades thin, deltate to lance-linear, 5-12 cm long by 1-5 mm wide, simple or 1-2 times pinnately lobed, the lobes lanceolate to lance-linear, margins entire or sharply serrate.

Flowers: Flower heads yellow, radiate, arranged in flat-topped panicles, on 4-6 cm peduncles; calyculi (extra set of bracts just below the involucre) of 8-17 green, linear, acute-tipped bractlets, these 3-6 mm long by 1 mm wide, with ciliate margins; involucre (ring of bracts wrapped around flower head) campanulate to hemispheric, 0.5 cm high by 1 cm wide, the bracts (phyllaries) 8-12, ovate to lanceolate, brown with yellow margins and tips; ray florets 5-6, the corolla laminae (ray petals) yellow, 1-3 cm long; disc florets 12-20, the corollas yellowish, 3-4 mm.

Fruits: Achenes dark brown to blackish, slightly quadrangular in cross-section, the faces weakly 2-grooved; with or without 2 erect to spreading, retrorsely barbed awns.

Ecology: Found in moist soil near streams, in marshes, or in seeps and springs from 3,000-6,000 ft (914-1829 m); flowers July-October.

Distribution: s AZ; south to Guatemala; adventive in France and Italy.

Notes: Bidens is a genus of herbaceous plants with opposite leaves, discoid or radiate flower heads with yellow-orange flowers, and seeds (achenes) with 2-4 barbed awns. B. aurea is distinguished by its variable leaf morphology, which ranges from simple to twice pinnately lobed, with edges that can be smooth or coarsely toothed; its flower heads with narrow, green outer bractlets (calyculi), wider yellow phyllaries, 5-6 showy yellow rays, and 12-20 yellow disc florets in the center of the heads; also the seeds which frequently lack the barbed awns that usually characterize this genus. Unlike many Bidens spp, this species is a perennial. Look for it in mid-elevation wetland and riparian habitats south of Tucson.

Ethnobotany: Unknown for this species, others in genus have many uses.

Etymology: Bidens is derived from the Latin bis, twice and dens, tooth, hence meaning 2-toothed, while aurea means golden, probably referring to the color of the phyllaries.

Synonyms: Bidens aurea var. wrightii, Bidens heterophylla, Coreopsis aurea

Editor: SBuckley 2010, AHazelton 2015