Limnocharis flava

Limnocharis flava (commonly known as yellow velvetleaf, sawah flower rush, sawah lettuce) is a species of aquatic flowering plant which is native to Mexico, Central America, South America, Cuba, Haiti and the Dominican Republic but widely naturalized in southern and southeastern Asia: India, Sri Lanka, Cambodia, Burma, Thailand, Vietnam, Indonesia, Malaysia, Brunei and southern China (Guangdong, Yunnan). Limnocharis flava is roughly 50 centimetres (20 in) tall growing in clumps. Its triangular-shaped leaves and hollow stems are glabrous. Its inflorescences have a very characteristic shape, producing three-lobed yellow flowers about 1.5 cm in diameter. The fruits are spherical. Although it is not a floating plant, its seeds are carried away by currents. Yellow velvetleaf grows generally wherever there is not very deep stagnant fresh water, in swampy areas. It sometimes invades rice fields where it can become a weed. As an invasive species it has become a pest in some wetlands in other parts of the world.

from Wikipedia