Description from Flora of China
Thymus serpyllum Linnaeus var. mongolicus Ronniger, Notizbl. Bot. Gart. Berlin-Dahlen 10: 890. 1930.
Stems numerous, trailing to ascending; vegetative shoots pubescent; fertile branches (1.5-)2-10 cm, densely retrorse pilose or slightly spreading pilose below inflorescences, sparsely fine pilose at base, 2-4-leaved. Petioles of lower stem leaves ca. 1/2 as long as blades; leaf blade ovate, 4-10 × 2-4.5 mm, glabrous, ± conspicuously glandular, base cuneate to attenuate, margin entire or 1- or 2-serrulate, apex obtuse to subacute. Inflorescences capitate; floral leaves ciliate on lower 1/3 of margin; bractlets deciduous at base. Calyx tubular-campanulate to narrowly campanulate, 4-4.5 mm, base pilose, apex subglabrous; teeth of upper lip less than 1/3 as long as lip, triangular, ciliate or glabrous; lower lip as long as to longer than upper. Corolla purple-red, purple, or reddish, 6.5-8 mm, sparsely pubescent; tube elongated, 4-5 mm, slightly dilated upward. Nutlets subglobose to ovoid, compressed. Fl. Jul-Aug.
* Stony hills, slopes, grassy areas, valleys; 1100-3600 m. Gansu, Hebei, Nei Mongol, Qinghai, Shaanxi, Shanxi.