Subshrubs, to 16 cm (rounded or flat-topped). Stems greenish to gray, much branched, pilose. Leaf blades 1-nerved, linear to acerose, 8-20 × 1-2 mm, scabrous to glabrescent. Peduncles 5-35 mm. Involucres campanulate, 3-5 × 5-7 mm. Phyllaries suborbiculate to oblong, becoming scarious proximally, appressed-hairy distally, apices obtuse, ciliate. Paleae uniformly yellow, apices obtuse, erose. Ray florets 4-7; corollas usually white, sometimes pale yellow, laminae oblong to suborbiculate, 7-10 mm. Disc florets 8-13; corollas yellow or tinged with purple (drying reddish), 3-6 mm, lobes 1 mm. Cypselae 2.4-4 mm, 3-angled (ray) or compressed (disc), ribbed, strigose or distally ciliate; pappi usually of 1-3 unequal awns, sometimes reduced to teeth. 2n = 20, 40, or 22.

Flowering spring-fall. Rocky open slopes, flats, calcareous soils; 700-1900 m; Ariz., N.Mex., Tex.; Mexico (Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Sonora, Zacatecas).

Attribution of Zinnia acerosa to Utah (S. L. Welsh et al. 1993) was based on Atwood et al. 9704 (BRY), from Moab, Grand County; the specimen was indicated as 'possibly cultivated' by the collector, and it is well outside the known range of the species.

FNA 2006, Wiggins 1964

Duration: Perennial Nativity: Native Lifeform: Subshrub General: Much branched low rounded or flat-topped subshrub 10-25 cm tall, with slender cinereous-puberulent branches, irregularly scaly grayish bark. Leaves: Linear to oblanceolate-linear, acerose leaves .3-2.5 mm wide, numerous, often longer than internodes, 5-20 mm long, cinereous-puberulent, golden punctate glands interspersed among hairs. Flowers: Peduncles 5-35 mm long, campanulate involucres 5-7 mm long, 3-5 mm wide; phyllaries suborbicular to oblong, greenish and tomentulose at first, later glabrate and stramineous but dull; ray flowers mostly 5-7, ligules suborbicular to broadly oblong, 7-10 mm long, white or faintly yellow, strongly green veined beneath, persist, strongly reflexed in fruit; disk corollas 5-6 mm, tinged with purple. Fruits: Disk cypselae 2.5-3.5 mm long, striate, strigose or only upwardly ciliate, pappus usually of 2-3 unequal awns or much reduced; ray achenes oblanceolate, 3-angled in cross-section, receptacular chaffy bracts uniformly yellow, erose at apex. Ecology: Found on dry slopes and flats and sometimes on calcareous soils; 3,000-7,500 ft (914-2286 m); flowers May-October. Distribution: e UT, AZ, s NM and sw TX; south to n MEX. Notes: A low-growing, mound-forming, perennial subshrub; distinguished by its stiff-hairy linear leaves with 1 vein (3 in Z. grandiflora); small number, 5-7 white ray flowers (yellow in grandiflora), few yellow disk flowers and rounded, ciliate phyllaries. Ethnobotany: Plant was crushed and used as a paste on swellings or aches. Also given to children to help them learn to talk. Etymology: Zinnia is named for Johan G. Zinn (1729-1759) a German botanist, while acerosa means sharp, or with stiff needles. Synonyms: Zinia pumila Editor: SBuckley 2010, FSCoburn 2015