Annuals, 10-80 cm (robust). Stems 1-25, usually purple-red-tinted proximally, sometimes throughout, often branched throughout, ± hairy. Leaves: blades simple or lobed (lobes 3-19+), ± hairy, gland-dotted; mid leaves lobed (lobes 5-11+, terminal lobes 0.3-1 mm wide). Heads 15-350+ per plant in paniculiform arrays. Peduncles 2-12 cm, sparsely hairy. Involucres subhemispheric to campanulate to ± urceolate, 6-10 × 7-12.5 mm. Phyllaries in 2 series, unequal; outer 8-13, basally connate ¹/4-¹/3 their lengths, obovate to oblanceolate, 3.5-5.2 mm, apices acuminate; inner 8-13, obovate, 3.8-5.9 mm, apices acuminate to acute. Ray florets 8-13; corollas yellow, 8.5-11 × 3-5.5 mm. Disc florets 50-150+; corollas 2.6-4.1 mm. Cypselae narrowly obpyramidal, 1.7-2.5 mm; pappi of 5-6 obovate, aristate scales 1.6-2.3 mm. 2n = 22, 24, 28, 30.

Flowering (Feb-)Apr-Jun(-Aug). Roadsides, open flats, mesquite and creosote-bush flats, ditches and drainage areas, stream banks and bottoms; 60-1500 m; Ariz., Calif., Colo., Kans., N.Mex., Okla., Tex.; Mexico (Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Sonora, Tamaulipas).

Duration: Annual

Nativity: Native

Lifeform: Forb/Herb

General: Annual herbs, 15-60 cm tall, bushy and aromatic, from a taproot; stems 1-25, usually purple-red-tinted proximally, sometimes throughout, often branched throughout, more or less hairy.

Leaves: Basal leaved usually withered by flowering; caluine leaves alternate; blades 1-10 cm long, pinnately lobed into 3-15 filiform segments, more or less hairy, gland-dotted.

Flowers: Heads radiate and yellow, in panicles of 15-350+ flower heads, on sparsely hairy peduncles; involucres subhemispheric to campanulate or urceolate, 6-10 mm high and 7-12 mm wide; phyllaries in 2 unequal series, the outer series united at the base for the 1/4 to 1/3 of their lengths, obovate to oblanceolate, 3-5 mm long; inner series of phyllaries not united at the base, obovate, 4-6 mm long; ray florets 8-13 per flower head, the laminae (ray petals) 8-11 mm long, yellow; disc florets 50-150+ per flower head, yellow.

Fruits: Achenes narrowly obpyramidal, 2 mm long; topped with a pappus of 5-6 obovate, aristate scales, 2 mm long.

Ecology: Found on roadsides, open flats, mesquite and creosote-bush flats, ditches and drainage areas, stream banks and bottoms, below 5,000 ft (1524 m); flowers (Feb-) Apr- June (-Aug).

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

Notes: Distinguished by being a robust annual herb branching throughout; leafy to densely leafy foliage of thinly divided, gland-dotted, sparsely hairy leaves with narrow, pointed lobes; yellow disks and white-yellow 3-lobed rays; hairy seeds resembling an inverted pyramid topped with a pappus of 5-6 broadening scales with pointed tips. Becomes abundant in overused rangeland; highly poisonous to livestock. It is noted to be pleasantly aromatic.

Ethnobotany: Used medicinally by indigenous tribes; a secondary compound, hymenovin, has been found to have anti-cancer properties.

Etymology: Hymenoxys comes from Greek hymen, meaning membrane, and oxys, meaning sharp or sharp pointed, referring to the awned pappus scales; odorata means possessing an odor.

Synonyms: Picradenia odorata, Hymenoxys chrysanthemoides subsp. osterhoutii, Hymenoxys multiflora

Editor: FSCoburn 2014, AHazelton 2017