Robust well branched herb, sometimes woody at the base or even shrubby, up to 400 cm tall, subglabrous, puberulent, or densely villous. Leaves linear to subovate, 2-14.5 cm long, 0.4-4 cm wide, narrowly or broadly cuneate at base, the apex attenuate; submarginal vein well developed; petioles up to 10 mm long. Sepals 4, ovate or lanceolate, 6-15 mm long, 1-7.5 mm wide. Petals yellow, broadly obovate or cuneate, emarginate, 5-17 mm long, 4-17 mm wide. Stamens 8, the epipetalous ones shorter; filaments 1-4 mm long; anthers 1.2-4 mm long, extrorse but soon crumbling and shedding pollen directly on the stigma. Pollen shed in tetrads. Discs slightly raised, with a white-hairy sunken nectary surrounding the base of each epipetalous stamen. Style 1.5-3.5 mm long; stigma subglobose, shallowly 4-lobed, 1.2-3 mm across. Capsule thin-walled, 17-45 mm long, 2-8 mm. thick, terete, pale brown with 8 darker ribs, readily and irregularly loculicidal; pedicel up to 10 mm long. Seeds pluriseriate in each locule of the capsule, free, brown, rounded, 0.6-0.75 mm wide including the inflated raphe which is equal in size to the body of the seed and evenly transversely ridged. 2n = 32, 48. Flowers Jan-Dec; fruit Jan-Dec.

TAIPEI: Kankou, Hsu 5242*; Shihpai, Chuang, Chao & Kao 4320. TAICHUNG: Tungshih, DeVol, Feung & Kao 4338. NANTOU: Sun Moon Lake, Ream 1-28. TAINAN: Matao, Morimoto s. n. 1941. KAOHSIUNG: Tabai, Hsu & Chuang 2414. PINGTUNG: Is. Hsiaoliuchiu, Hosokawa 1725; Mutan, Cheng 1459. TAITUNG: Is. Lanyu, Huang & Kao 5367.

Throughout the tropics and subtropics of the World, in moist places as about streams, swamps, ponds, and lakes at low elevations.

The distinctions between subsp. sessiliflora, with long erect hairs and broader leaves, and subsp. octovalvis, with appressed or sparse pubescence and narrower leaves, no longer seem useful either in Taiwan, where both forms are frequent, or elsewhere; little geographical distinction is evident.