Cassia fistula

Flower bud of golden shower tree

Cassia fistula, known as the golden shower tree and by other names, is a flowering plant in the family Fabaceae. The species is native to the Indian subcontinent and adjacent regions of Southeast Asia. It ranges from southern Pakistan eastward throughout India to Myanmar and Thailand and south to Sri Lanka. It is closely associated with the Mullai region of Sangam landscape. It is the national tree of Thailand, and its flower is Thailand's national flower. It is also the state flower of Kerala in India and of immense importance amongst the Malayali population. It is a popular ornamental plant and is also used in herbal medicine.

Source: http://en.wikipedia.org/wiki/Cassia_fistula