Description from Flora of China
Mazus fargesii Bonati, M. japonicusBonati (1908), not Kuntze (1891); M. miquelii Makino var. stolonifer (Maximowicz) Nakai; M. rugosus Loureiro var. stolonifer Maximowicz; M. stolonifer (Maximowicz) Makino; M. wilsonii Bonati; Vandellia japonica Miquel.
Perennials, glabrous or sparsely villous. Primary root short; fibrous roots numerous, clustered. Stems erect to obliquely ascending, 10-15 cm; stolons to 15-20 cm, rooting from nodes or not. Basal leaves numerous, rosulate, petiolate; leaf blade obovate-spatulate, 3-7 cm including petiole, margin coarsely serrate, sometimes pinnatisect. Stem leaves on erect stems alternate, on stolons mostly opposite; petiole short; leaf blade ovate to subrounded, 1.5-4 cm including petiole, less than 2 cm wide, margin sparsely serrate. Racemes terminal, elongated, lax. Pedicel gradually shorter toward inflorescence apex, lower ones to 2 cm. Calyx campanulate-funnelform, 7-10 mm; lobes lanceolate-triangular, as long as tube. Corolla purple or white with purplish spots, 1.5-2 cm; lower lip middle lobe obovate, shorter than lateral lobes and slightly exserted; upper lip erect, short. Capsule globose, slightly exserted. Fl. and fr. Feb-Aug.
Trailsides in wet places, sparse forests; below 300 m. Anhui, Fujian, Guangxi, Hubei, Hunan, Jiangsu, Jiangxi, Taiwan, Zhejiang [Japan].