Description from Flora of China
Annuals, 5-25 cm tall, often many branched from base; main stems erect; branches diffuse, entirely glabrous or densely glandular pubescent. Leaves sessile, lower ones oblanceolate, upper narrowly oblong, 1-2.5 cm X 2-6(-8) mm, margin entire or deltoid dentate above middle. Racemes terminal and axillary, elongated, lax, to 20 cm in fruit; bracts alternate, similar to but slightly smaller than leaves. Pedicel less than 2 mm. Calyx 4-lobed; lobes broadly linear to narrowly oblong, 3-4 mm. Corolla white or pale blue, rotate, ca. 2 mm; lobes narrowly oblong to ovate. Stamens shorter than corolla. Capsule obcordate, strongly compressed, 3-4 mm, wider than long, margin short glandular ciliate, apex conspicuously notched. Style 0.2-0.3 mm, included in notch. Seeds ca. 40 per capsule, oblong, flattened, convex on both sides, smooth. Fl. May-Jun. 2n = 52.
Moist waste lands, roadsides; below 3000 m. Native to North America, naturalized in Anhui, Fujian, Guangxi, Guizhou, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Shandong, Sichuan, Xizang, Yunnan, Zhejiang [Japan, Korea, Mongolia, Russia; Europe].