Description from Flora of China
Erythraea japonica Maximowicz, Bull. Acad. Imp. Sci. Saint-Petersbourg, ser. 3, 31: 67. 1886.
Plants 5-30 cm tall, glabrous. Stems much branched. Basal leaves short petiolate; leaf blade spatulate, 1-2 cm × 8-10 mm including petiole, base narrowed, apex rounded, veins 1-3 and abaxially prominent. Stem leaves sessile, oblong, elliptic, or ovate-elliptic, 0.8-2.2 cm × 3-12 mm, base rounded and nearly clasping, apex obtuse to rounded; veins 1-3, prominent. Cymes spicate. Flowers sessile. Calyx tubular, 3-4 mm; lobes linear to narrowly elliptic, 6-8 mm, apex obtuse, midvein prominent. Corolla white outside, pink inside, 1-1.3 cm, tube narrowly tubular; lobes narrowly oblong, 3-5 mm, margin entire or serrulate, apex obtuse. Filaments 1.5-2 mm; anthers ellipsoid, 0.5-0.7 mm. Style 3-3.5 mm. Capsules narrowly ellipsoid, 8-10 mm. Seeds dark brown, globose, 0.3-0.5 mm in diam. Fl. and fr. May-Jul.
Weed in cultivated land. Taiwan [Japan].