Description from Flora of China
Annuals. Stem 10-50 cm tall, erect or decumbent, not rooting at nodes, with 0.1-0.3 mm patent nonglandular trichomes and 0.1-0.2 mm patent glandular trichomes. Stipules lanceolate, distinct. Leaves opposite; petiole with 0.1-0.3 mm patent nonglandular trichomes and 0.1-0.2 mm patent glandular trichomes; leaf blade 1.5-3.8 cm, palmately cleft, ratio of main sinus/middle segment length = 0.3-0.75, pilose with appressed nonglandular trichomes; segments 5, obtriangular, 2-4 mm wide at base, 3(-5)-lobed at apex, ratio of second sinus/middle segment length = 0.16-0.29. Cymules solitary, 2-flowered; peduncle 0.5-3.2 cm. Pedicel 0.6-1.6 cm, with 0.1-0.3 mm patent nonglandular trichomes and 0.1-0.2 mm patent glandular trichomes; bracteoles linear-lanceolate. Sepals 3-4.5 mm, mucro ca. 0.1 mm, ratio of mucro/sepal length = 0.02-0.03, outside with 0.6-1 mm patent nonglandular trichomes and 0.2-0.5 mm ± patent nonglandular and glandular trichomes, outside glabrous. Petals pale purple, 2-3 mm, erect to patent, both surfaces glabrous, margin basally ciliate, apex emarginate with a 0.2-0.5 mm notch. Stamens external whorl lacking anthers and reduced to 5 staminodes; filaments white, lanceolate, abaxially pilose and proximal half ciliate, trichomes 0.1-0.2 mm; anthers purplish, ca. 0.3 mm. Nectaries 5, hemispheric, glabrous. Stigma yellowish. Fruit 0.9-1.1 cm, erect when immature; mericarps smooth, without a basal callus, with to 0.2 mm appressed nonglandular trichomes, base with a few cilia; rostrum 7-9 mm, without a narrowed apex; stigmatic remains 0.5-0.7 mm. Seeds 1.7-1.8 mm. Fl. Jun-Jul, fr. Aug-Oct. 2n = 26.
Although found as a naturalized weed in Taiwan, this species could be found as a native plant near the W boundaries of China, because its natural area includes the W Himalayas. This species also grows as an introduced weed in America and Australia.
Open habitats, dry grassland, cultivated and waste places; 1800-2300 m. Naturalized in Taiwan [native to Afghanistan, W Asia, Europe, Kashmir, Kazakhstan, Kyrgyzstan, Russia, Tajikistan, Turkmenistan, Uzbekistan].