Shrub ambassador introduced to new padre (7)
I believe the answer is:
ephedra
'shrub' is the definition.
(I know that ephedra is a type of shrub)
'ambassador introduced to new padre' is the wordplay.
'ambassador' becomes 'HE' (His or Her Excellency).
'introduced to' means one lot of letters goes inside another.
'new' indicates an anagram.
'padre' is an anagram of 'epdra'.
'he' put within 'epdra' is 'EPHEDRA'.
(Other definitions for ephedra that I've seen before include "desert plant" , "Source of asthma medication" .)