Subshrubs or shrubs, green, to 25 cm, usually puberulent, sometimes glabrescent, rarely glabrous. Stems erect (branched from bases). Leaves mostly opposite; blades not lobed, linear to acerose, 10-18 mm. Peduncles 0-10 mm, puberulent or glabrous. Calyculi of 5 lance-linear bractlets, lengths 1/2+ phyllaries. Involucres campanulate to cylindric, 5-7 mm. Phyllaries ca. 13, margins of outer distinct less than 1/6 their lengths, abaxial faces puberulent or glabrous. Ray florets 7-8; corollas lemon-yellow, laminae 5-6 × 2-3 mm. Disc florets 18-25+; corollas pale yellow, 3-4 mm. Cypselae 3-3.5 mm; pappi of ca. 20 scales (each a fascicle of 3-5 bristles), 3-4 mm. 2n = 16, 24. Flowering through the year, mostly summer-fall. Calcareous outcrops, gypseous soils; 1000-2000+ m; Ariz., Nev., N.Mex., Tex., Utah; Mexico.
FNA 2006, Martin and Hutchins 1980, Heil et al. 2013
Duration: Perennial Nativity: Native Lifeform: Subshrub General: Aromatic subshrubs, to 25 cm tall, from a strong, woody taproot; stems woody at the base, erect to spreading, densely branching, glabrous to slightly villous. Leaves: Mostly opposite along the stems; blades linear to filiform, 1-2 cm long, sparsely scaberulous with scattered glands; usually with fascicles of smaller leaves in the axils. Flowers: Flower heads yellow and radiate, sessile or on short peduncles less than 1 cm long; involucres campanulate to cylindric, 5-7 mm high, the bracts (phyllaries) 8-14, fused together almost to the tips, gland-dotted; with calyculi (extra set of bracts below the flower head) of 5 much smaller bractlets; ray florets 7-8 per flower head, the laminae (ray petals) 5-6 mm long, yellow; disc florets 18-25 per flower head, pale yellow. Fruits: Achenes 3 mm long, cylindric; topped with a pappus of 20 scales, these dissected at the apex into 3-5 slender bristles. Ecology: Found in sandstone or limestone soils, on rocky slopes, mesas and low rolling hills, from desert scrub and pinyon-juniper communities, from 3,500-6,000 ft (1067-1829 m); flowers June-October. Distribution: s NV, s UT, AZ, NM, sw TX; south to s MEX. Notes: A low-growing, much-branched subshrub, often forming mounds; distinguished by the short, needle-like, resinous-sticky, fragrant leaves; small but showy yellow flower heads; and the amber to clear glands which look like oil droplets scattered on the leaves and phyllaries. It is often a plant of calcareous or gypsum soils. Distinguish from T. pentachaeta by the leaves and the locations of the flowers; T. acerosa has simple, linear, needle-like leaves 1-2 cm long, and sessile to subsessile flowers that are embedded in the foliage, while T. pentachaeta has leaves that are pinnately divided into 3-7 needle-like lobes, and flowers that are held above the foliage on peduncles 2-10 cm long. Ethnobotany: Used for fevers and to flavor tobacco. Etymology: Thymophylla is from the Greek thymos, thyme, and phyllon, for leaf, alluding to the similarity to the leaves of the thyme plant; acerosa means sharp, or with stiff needles, also referring to the leaves. Synonyms: Dyssodia acerosa Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2017