On which Spartans perhaps grow replete, possibly after adult pressure (5-4)
I believe the answer is:
apple-tree
'on which spartans perhaps grow' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'replete possibly after adult pressure' is the wordplay.
'possibly' is an anagram indicator.
'after' says to put letters next to each other.
'adult' becomes 'a' (abbreviation).
'pressure' becomes 'p' (scientific abbreviation).
'replete' with letters rearranged gives 'pletree'.
'a'+'p'='ap'
'pletree' after 'ap' is 'APPLE-TREE'.
Can you help me to learn more?
(Other definitions for apple-tree that I've seen before include "It might produce Cox" , "Plant bearing pippins" , "Perennial woody plant bearing fruit for cooking or eating -Granny Smiths?" , "Source of the growth that inspired Newton?" .)