He's really missed the combination of today's themes (9)
I believe the answer is:
araucaria
'he's really missed' is the definition.
(late Guardian crossword setter Araucaria)
I can't explain the remainder of the clue.
(Other definitions for araucaria that I've seen before include "Monkey puzzle tree - Guardian cryptic crossword setter" , "Evergreen" , "Coniferous tree" , "puzzle for primates?" , "Monkey puzzle tree (or Chile pine)" .)