Old boss purchases northern plant (8)
I believe the answer is:
oleander
'plant' is the definition.
The answer is an example.
'old boss purchases northern' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'boss' becomes 'leader' (I've seen this in another clue).
'purchases' is an insertion indicator.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'leader' going around 'n' is 'leander'.
'o'+'leander'='OLEANDER'
(Other definitions for oleander that I've seen before include "No dealer in evergreen shrub" , "Flowering plant" , "Evergreen flowering shrub from olden era" , "Mediterranean shrub" , "Flowering shrub from olden era, oddly" .)