Trees spring up round South (4)
I believe the answer is:
asps
'trees' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.
'spring up round south' is the wordplay.
'spring' becomes 'spa' (spa can mean a mineral spring).
'up' is a reversal indicator (in down clue: letters go upwards).
'round' indicates putting letters inside.
'south' becomes 'S' (abbreviation).
'spa' back-to-front is 'aps'.
'aps' placed around 's' is 'ASPS'.
Can you help me to learn more?
(Other definitions for asps that I've seen before include "poisonous things" , "native Africans?" , "Pass (anag)" , "Poisonous snakes" , "Small vipers" .)