Extreme characters crushing a meadow plant (6)
I believe the answer is:
azalea
'plant' is the definition.
'extreme characters crushing a meadow' is the wordplay.
'extreme characters' becomes 'az' (I've seen this in other clues).
'crushing' means one lot of letters go next to another (in a down clue, some letters bear down upon others).
'meadow' becomes 'lea' (I've seen this before).
'az'+'a'+'lea'='AZALEA'
(Other definitions for azalea that I've seen before include "Rhododendron subgenus" , "Rhododendron-like plant" , "Rhododendron-type shrub" , "Acid-loving plant" , "flower" .)