Subglabrous herb, creeping and rooting at the nodes, the stems at most ascending decumbent, finely puberulent, up to 40 cm or perhaps more in length, matted. Leaves ovate to elliptic ovate, 0.5-2.5 cm long, 0.4-2 cm wide, abruptly narrowed to a winged petiole up to 7 mm long, or subsessile, glabrous, the apex acute; main veins 4-7 on each side of midrib; submarginal vein absent. Flowers axillary. Sepals 4, deltoid-acute, 1-3 mm long, 1-1.7 mm wide, very finely puberulent along margins. Petals 0. Stamens 4; filaments translucent, 0.5-0.8 mm long, dilated below; anthers 0.6-0.9 mm long and wide, nearly basifixed, dull yellow, the connective orange on its abaxial side; anthers introrse, shedding pollen directly on the stigma at anthesis. Pollen grains shed singly. Disc raised 0.1-0.2 mm high, glabrous, prominently 4-lobed, green, the lobes opposite the petals. Style green, 0.6-1 mm long; stigma dark green, globose, 0.3- 0.5 mm thick. Capsules elongate-globose, 3-5 mm long, 2.5-3.5 mm thick, finely puberulent, corky-walled but readily and irregularly loculicidal, on a short pedicel. Seeds pluriseriate in each locule of the capsule, free, light or glossy red-brown, 0.7-0.9 mm long, the body 0.35-0.4 mm thick, apiculate; raphe inflated, 0.2-0.5 mm across, coarsely reticulate. 2n = 32. Flowers Apr-Aug; fruit Apr-Aug.
TAIPEI: Tatunshan, Peng 9496; Fushan, Peng 15149. HSINCHU: Hukou, Shimada 4944. ILAN: Mingchih, Hsiao s. n. 1988; Nanao, Peng 13816. PINGTUNG: Mutanwan, Matuda s. n. 1919; Nanjenshan, Peng 7795.
Central and southern Japan, north China, and Taiwan. Rare and local in moist places, especially on the beds and along borders of lakes and ponds, flowering when these dry out in late summer.
