Which is the national flower of Thailand ?

Which is the national flower of Thailand ?

A. Rose
B. Lily
C. Yellow Elder
D. Ratchaphruek

Known locally as the ratchaphruek, the official botanical name of the tree bearing Thailand’s national flower is the Cassia Fistula Linn. The tree might also be called the chaiyaphruek and the actual flower may be referred to as dok koon.