Snake destroyed diarist's plant (10)
I believe the answer is:
aspidistra
'plant' is the definition.
(aspidistra is a kind of plant)
'snake destroyed diarist's' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'destroyed' is an anagram indicator.
'diarist' with letters rearranged gives 'idistra'.
'asp'+'idistra'='ASPIDISTRA'
(Other definitions for aspidistra that I've seen before include "Huge house plant" , "Iris adapts (anag) - indoor plant" , "Large houseplant" , "leafy plant" , "For Asian native" .)