Premise: 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 and southern China (Guangdong, Yunnan).
Hypothesis: Vietnam is home to the sawah flower.