Just to add to the information by Dr. Stephen, the bracketed author is
often referred to as the author of the basionym.
Thank you very much Dr. Stephen. Very informative links which has also lead me to explore related areas in books.
Thank you very much Dr. Pankaj for bringing in your perspective. As I read I realize that there is an entirely new group of taxonomists who in 1998, have come up with a revised system of classification, and I believe it is followed in some syllabus abroad based on DNA sequence and cladistic information.
I have learned a little bit of the two families you have mentioned, Apocynaceae and Asclepiadaceae after having seen some of the plants in the forests and parks from both the families in Mumbai, and refering to the book by Prof. R.N. Sutaria (1969), pg: 305 to 333. Here the main diferences have been listed by the author some of which are : Leaves opposite or whorled, exstipulate, the presence of intramarginal vein present, milky or watery juice in Apocynaceae. Leaves opposite, decussant, simple, entire, exstipulate, intramarginal vein not present in Asclepiadaceae.
Apocynaceae not succulent in habit whereas Asclepiadaceae is mostly succulent and so on. So they look distinct to me.