An annual originating in North America grows in wetlands along
rivers, edges of ponds or swamps, paddy fields, or the like. Stems,
four-ridged, stand erect and branch well to grow to 80-100cm in
height. Leaves are in an alternate arrangement, 5-12cm long, 1.5-3cm
wide, lanceolate to narrow oblong, with next-to-nothing petioles,
and bases becoming wings connecting to the stem's ridges. Flowers,
yellow 4-petaled, about 3cm in diameter, singly appear at axils and
open flat. Bloom time: August-October.