Plant science's leading character featured in talk (7)
I believe the answer is:
parsley
'plant' is the definition.
(parsley is a kind of plant)
'science's leading character featured in talk' is the wordplay.
'leading character' says to take the initial letters.
'featured in' is an insertion indicator.
'talk' becomes 'parley' (to parley is to talk with an enemy).
The first letter of 'science' is 's'.
's' inserted inside 'parley' is 'PARSLEY'.
(Other definitions for parsley that I've seen before include "Herb for garnishing" , "Cow -, fool's - and stone - are all plants" , "Use the herb sparely" , "plant used in cooking" , "Culinary herb" .)