Description from Flora of China
Herbs, perennial or ?annual. Stems numerous, herbaceous or woody, woolly, glandular pilose, or pilose. Leaves opposite, scalelike below, gradually increasing in size upward, sessile, margin entire. Racemes terminal or flowers solitary and axillary. Bracteoles 2, linear-lanceolate, adnate to base of calyx tube. Calyx tubular; lobes 4 (5 in M. monantha), linear-lanceolate. Corolla 2-lipped; upper lip somewhat reflexed or galeate. Stamens 4, didynamous; anthers dorsifixed, 2-loculed; locules oblong, divergent, mucronate. Ovary incompletely 2-loculed. Capsule ovoid, 4-furrowed, dehiscing along dorsal suture of carpel, usually enclosed by persistent calyx. Seeds numerous.
Two species: China, Japan; both in China.
According to Hemsley (Forbes & Hemsley, J. Linn. Soc., Bot. 26: 203. 1889) there is a third species in Guangdong, Monochasma monantha Hemsley, with 5-lobed calyx and solitary,
terminal or pseudo-terminal flowers, but we have not seen any specimens.