This plant is given the name A. intrusa in the book "1001 Garden Plants in Singapore". However, in the GRIN database, A. intrusa is a synonym of A. gangetica. Also, the flower of the actual A. gangetica   looks quite different from that of the plant called A. intrusa. I am unable to find a good reference that explains the differences between the 2 names. For the time being, I have followed the classification of the GRIN database and keep A. intrusa as a synonym.