Annuals, (10-)20-80+ cm. Leaves: petioles 5-25 mm; blades rounded-deltate overall, 25-90+ × 15-35+ mm, (1-)2(-3)-pinnatisect, ultimate lobes lance-rhombic or ovate to lanceolate, 15-30(-50+) × 5-15(-30+) mm, bases truncate to cuneate, ultimate margins entire or ± serrate to incised, usually ciliolate, apices obtuse to acuminate, faces glabrous. Heads usually borne singly, sometimes in open, ± corymbiform arrays. Peduncles (10-)30-50(-150+) mm. Calyculi of 8-13 usually spreading, narrowly lanceolate, oblanceolate, or subulate to linear bractlets 2-5 mm, margins entire, usually ciliate, abaxial faces usually glabrous. Involucres ± campanulate, 2.5-5+ × 1.5-3(-4) mm. Phyllaries 8-13+, lanceolate, (3-)4-6+ mm. Ray florets 0 or 1(-5+); laminae whitish, 1-3(-7) mm. Disc florets 13-25+; corollas yellowish, 1-2 mm. Cypselae: outer red-brown, obcompressed, cuneate, 6-7 mm, margins not ciliate, apices truncate, faces 2-grooved, antrorsely tuberculate-hirtellous; inner dark brown to blackish, ± equally 4-angled, linear-fusiform, 10-14 mm, margins not ciliate, apices ± attenuate, faces glabrous; pappi of 2(-3), erect, retrorsely barbed awns (1-)2-4 mm.

Flowering Sep. Along streams, other wettish sites; 900-2000 m; Ariz., Colo., N.Mex., Okla., Tex.; Mexico.

Duration: Annual

Nativity: Native

Lifeform: Forb/Herb

General: Annual herb, 20-80 cm tall; stems glabrous or glabrate, usually branched.

Leaves: Opposite, on petioles 5-25 mm long; blades 2-9 cm long by 1-4 cm wide, rounded-deltate in outline, twice or thrice pinnately dissected, ultimate margins serrate or incised, faces glabrous.

Flowers: Flower heads orange and white, discoid or radiate, borne singly or in open, flat-topped panicles, on peduncles 3-5 cm long; calyculi (extra set of bracts just below the involucre) of 8-13 spreading, narrowly lanceolate bractlets, 2-5 mm long, with ciliate margins; involucre (the ring of bracts surrounding the flower head) campanulate, 2-5 mm long by 1-3 mm wide, the bracts (phyllaries) 8-13, lanceolate; ray florets absent or 1-5, the corolla laminae (ray petals) white, 1-3 mm long; disc florets 13-25, corollas yellowish-orange, 1-2 mm long.

Fruits: Outer (ray) achenes red-brown, flattened, 6-7 mm long; inner (disc) achenes dark brown to black, 4-angled, linear-fusiform, 10-14 mm long; all achenes have a pappus of 2 erect, retrorsely barbed awns, 2-4 mm long, attached to the top.

Ecology: Found in wet soils along streams, seeps, and springs from 4,000-6,500 ft (1219-1981 m); flowers July-October.

Distribution: AZ, NM, CO, OK, TX; south to MEX.

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. bigelovii is an annual herb found in middle and high elevation streamside habitats; with dissected leaves that are triangular in outline and have toothed edges; and small orange flower heads that sometimes have a few white ray flowers (these are the -petals- around the outside). Most other Bidens lack ray florets or else have yellow to orange rays. B. lemmonii can have whitish rays but the leaves of that species are dissected into narrower lobes, less than 5 mm wide, and the flower heads are usually sessile or on very short, 1-2 cm peduncles. B. leptocephala can also have whitish rays (usually yellowish), but that species has a narrow, cylindric flower head with fewer than 13 disc florets, while B. bigelovii has a wider campanulate flower head with 13-25 disc florets.

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 bigelovii is named for Dr. John Milton Bigelow (1804-1878) who collected under Whipple on the Pacific Railroad Survey of 1853-1854.

Synonyms: None

Editor: SBuckley 2010, AHazelton 2015