Perennials or subshrubs, ± grayish to green, to 15(-25) cm, usually puberulent to canescent, sometimes glabrescent or glabrous. Stems erect or spreading. Leaves mostly opposite; blades mostly pinnately lobed, 6-28+ mm overall, lobes 3-11 linear to filiform (usually stiff, setiform). Peduncles 20-100 mm, puberulent or glabrous. Calyculi 0, or of 1-5 deltate bractlets, lengths less than 1/2 phyllaries. Involucres obconic to campanulate or hemispheric, 4-6 mm. Phyllaries 12-21, margins of outer distinct 1/5 to nearly all their lengths, abaxial faces puberulent or glabrous. Ray florets (8-)12-21; corollas yellow to orange-yellow, laminae 2-6(-8) × 1-3 mm. Disc florets 16-40 or 50-80; corollas yellow, 2-4 mm (tending to zygomorphy in peripheral florets in some plants). Cypselae 2-3 mm; pappi of 10 erose and/or aristate scales mostly 1-3 mm.
FNA 2006, Martin and Hutchins 1980, Heil et al. 2013
Duration: Perennial Nativity: Native Lifeform: Subshrub General: Mildly aromatic perennial herbs to subshrubs, to 25 cm tall, from a woody taproot; stems erect, densely branched, grayish to green, usually densely puberulent. Leaves: Opposite and crowded along the stems; blades 1-3 cm long, pinnately divided into 3-7 stiff, sharp, linear to filiform lobes, these less than 1 mm wide, sparsely hairy and conspicuously gland-dotted. Flowers: Flower heads yellow and radiate, held above the leaves on slender peduncles 2-10 cm long; involucres cylindric, obconic, campanulate or hemispheric, 4-6 mm high, the bracts (phyllaries) 12-21 in 2 subequal series; outer phyllaries ciliate and fused to the inner phyllaries; inner phyllaries fused to each other, irregularly toothed at apex; ray florets 12-21 per flower head, the laminae (ray petals) 2-6 mm long, yellow-orange; disc florets 16-80 per flower head, yellow. Fruits: Achenes 2-3 mm long, black, linear; topped with a pappus of 10 irregularly toothed scales, 1-3 mm long. Ecology: Found on dry slopes and flats, especially on limestone soils, from 3,500-5,500 ft (1067-1676 m); flowers May-August. Distribution: s CA, s NV, AZ, s NM, s TX; south to s MEX; also in S. America. Notes: A low-growing perennial with a slightly woody base and small but showy yellow flower heads; note the translucent to amber oil glands on leaves and phyllaries; and the narrow, lobed leaves which are pleasantly fragrant when crushed. Distinguish from T. acerosa 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. T. pentachaeta is also usually not as robust as T. acerosa. There are two varieties in the region. Var. hartwegii has cylindric involucres, 2-3.5 mm wide, with 16-40 disc florets; it is found in AZ, NM, and TX. Var. belendium has campanulate to hemispheric involucres, 4-5 mm diameter, with 50-80 disc florets; it occurs from CA and NV east to TX Ethnobotany: Decoction of the root taken as a purgative. Etymology: Thymophylla is from the Greek thymos, thyme, and phyllon, for leaf, alluding to the similarity to the leaves of the thyme plant; pentachaeta comes from Greek penta for five, and chaeta for bristle or long hair, referring to the teeth on the pappus scales. Synonyms: Dyssodia pentachaeta Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2017