Description from Flora of China
Acetosella corniculata (Linnaeus) Kuntze; Oxalis corniculata f. erecta Makino; O. corniculata subsp. repens (Thunberg) Masamune; O. corniculata var. repens (Thunberg) Zuccarini; O. corniculata subsp. subglabra (Kuntze) Masamune; O. corniculata var. taiwanensis Masamune; O. minima Steudel; O. procumbens Steudel; O. repens Thunberg; O. repens var. erecta (Makino) Masamune; O. repens f. speciosa Masamune; O. taiwanensis (Masamune) Masamune; Xanthoxalis corniculata (Linnaeus) Small; X. corniculata var. repens (Thunberg) Nakai; X. repens (Thunberg) Moldenke.
Annuals or short-lived perennials. Stems to 50 cm but often shorter, creeping, ascending to semierect, variably pubescent with adpressed simple hairs. Rootstock a slender taproot, sometimes woody; stems several, freely rooting at nodes in contact with soil; stolons absent. Stipules small, rectangular to auriculate. Leaves alternate or pseudoverticillate; petiole 1-8(-13) cm; leaflet blades obcordate, 0.3-1.8 × 0.4-2.3 cm, green or suffused purplish red, variably adaxially and abaxially pubescent, apex deeply emarginate. Inflorescences umbellate, (2-)1-5(-7)-flowered; peduncle usually slightly longer than petioles; bracts linear-lanceolate, 2-4 × ca. 1 mm. Pedicel 4-15(-20) mm, deflexed or horizontal in fruit, densely strigose. Sepals oblong-lanceolate, 3.5-5 × 1.2-2 mm, margin ciliate especially at apex. Petals bright yellow, oblong-obovate, 6-8 × 3-4 mm. Capsule long cylindric, 8-25 × 2-3 mm, 5-sided, strigose with abundant simple hairs and a few septate hairs on dehiscence sutures. Seeds brown to brownish red, 5-14 per locule, ovoid-oblong, 1-1.5 × 0.8-1 mm, transversely ridged. Fl. and fr. Feb-Oct. 2n = 24.
This species is used medicinally.
This highly successful weedy species is so widespread, particularly in areas disturbed by humans, that its origin is unknown. It has been reported from China in additional provinces, such as Heilongjiang, Jilin, Ningxia, and Xinjiang, where it is likely a weed in protected locations, such as in greenhouses. The most frequently encountered variety in China is Oxalis corniculata var. villosa (M. Bieberstein) Hohenacker, but this variety is often under-recorded due to the glabrescent nature of the adaxial surface of the leaves. Oxalis corniculata var. villosa has leaflet blades covered with trichomes all over the abaxial surface, whereas for var. corniculata the abaxial surface has trichomes only on the midrib of the terminal leaflet and the basal half of the lateral leaflets. Plants with leaves, and to a lesser extent all vegetative parts, suffused purplish red are Oxalis corniculata var. atropurpurea Planchon. The purple coloration is conspicuous in plants from exposed sunny habitats but is much less prominent in shaded plants and fades on drying, making confident determination of old herbarium specimens difficult. Determination of the exact distribution of these varieties in China needs additional study.
Synonyms of Oxalis corniculata var. villosa include: Oxalis villosa M. Bieberstein, Fl. Taur.-Caucas. 1: 355. 1808; Acetosella corniculata var. villosa (M. Bieberstein) Kuntze; ?O. corniculata f. maritima Masamune; O. corniculata var. sericea Knuth; O. corniculata var. trichocaulon H. Léveillé; O. corniculata f. villosa (M. Bieberstein) Goiran; ?O. corniculata var. viscidula Wiegand; O. langloisii (Small) Fedde; O. thunbergiana Montrousier; Xanthoxalis langloisii Small. Synonyms of Oxalis corniculata var. atropurpurea include: Oxalis corniculata f. purpurea (Parlatore) Knuth; O. corniculata var. purpurea Parlatore; O. tropaeoloides Schlachter ex Planchon; Xanthoxalis corniculata f. atropurpurea (Planchon) Nakai; X. corniculata var. atropurpurea (Planchon) Moldenke; X. corniculata f. purpurea (Parlatore) Nakai.
Mountain slopes, forests, grasslands, riversides, roadsides, fields, wastelands; sea level to 3400 m. Anhui, Chongqing, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Henan, Hubei, Hunan, Nei Mongol, Jiangsu, Jiangxi, Liaoning, E Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Bhutan, India, Japan, Korea, Malaysia, Myanmar, Nepal, Pakistan, Russia, Thailand; almost cosmopolitan].