Thanks Aditya ji, Parjanya ji, Gurcharan ji
This certainly is Emilia sonchifolia
also known aslilac tasselflower,
Purple Sow Thistle, Flora's paint brush,
Native to Asia
Asteraceae - Tribe Senecioneae.
The flowers open only that much as shown in the pictures. The achenes mature rapidly and the blown out cluster of seeds with feathery hairy puff can often be seen on the same plant.
The main characteristic is the leaf pattern- Arrow shaped, Sessile with auricles clasping the stem is unmistakable.
Anybody wants to add/correct anything.....Welcome
The elaborate description can be read on FOI website.http://www.flowersofindia.net/catalog/slides/Purple%20Sow%20Thistle.html
Dr Satish Phadke