Is this bunch at the top going to turn into bracts or leaves?
The clarity of the anatomical leaf and flower (bract) and thorn distribution of the Bougainvillea as brilliantly answered by 'down to earth digs' determines by the simplification of the helpful answer - not found anywhere else on the web pertaining to the Bougainvillea!
The thorns on a Bougainvillea are located at the base of each leaf, this should help you determine what is a leaf.
The flower is a tube like structure and is insignificant.
The bracts form around the flower in a cluster of 3.