Daughter is sitting on plant -- catastrophe! (8)
I believe the answer is:
disaster
'catastrophe' is the definition.
(synonyms)
'daughter is sitting on plant' is the wordplay.
'daughter' becomes 'dis' (I've seen this in other clues).
'is sitting on' is a charade indicator (letters next to each other).
'plant' becomes 'aster' (aster is a kind of plant).
'dis'+'aster'='DISASTER'
(Other definitions for disaster that I've seen before include "awful situation" , "Catastrophe, tragedy" , "Great tradegy or cataclysm" , "Terrible calamity" , "Event causing great damage" .)