Plant knocked over in dark office (4)
I believe the answer is:
okra
'plant' is the definition.
(okra is a kind of plant)
'knocked over in dark office' is the wordplay.
'knocked over' says the letters should be written in reverse.
'in' indicates the answer is hidden within the clue.
'arko' is hidden in the letters of 'dark office'.
'arko' written backwards gives 'OKRA'.
(Other definitions for okra that I've seen before include "vegetable soup ingredient" , "Lady's fingers; gumbo; bhindi" , "Long green tropical vegetable" , "old ladies' fingers" , "Edible seed pods" .)