Punnaga, Surapunnaga & Nagakesara are different plants. (Calophyllum inophyllum, Ochrocarpus longifolius & Messua ferrua respectively).
Nagakesara is floral parts ie kesara- Stamens are useful in Indian Medicine. In market floral parts of all three plants are sold in the name of Nagakesara. First two are substitutes of of third ie Nagakesara.
All are beautiful trees flowers.
pUjitaH pumAn iti punnAgaH (Comn. on Nighantusesha .- VrikshaKhanda 26-27)
(Refer. e-Nighantu CD containig 25 Ayurvedic Nighantus published by Central Council for Research in Ayurvedic Sciences, New Delhi