Largest flower

 World's largest flower 



The tropical rainforests of Indonesia and Malaysia are home to some unique, rare and endangered vegetation. Two very unique (read strange) species found here are 1. Amorphophallus titanum and 2. Rafflesia arnoldii. Both species have gigantic blooms with a characteristic foul smell which attracts pollinators, hence battling for the title of Corpse plant. 
Since the question is about the biggest flower, the answer would have to be Rafflesia arnoldii, is a single bloom 3 feet in diameter weighing around 11 kilograms. It is a parasitic plant devoid of chlorophyll, deriving nutrition from the host plants in the surrounding area. 

source http://lot10hotel.com/gunung-gad...
you can check this link for more information about the plant and its pollination. 
Amorphophallus titanum which is over 10 feet in height although larger than Rafflesia, it is the inflorescence (an aggregation of buds, not a single flower) that makes it the largest inflorescence in the world.