Vegetable providing standard crop (7)
I believe the answer is:
parsnip
'vegetable' is the definition.
(parsnip is a type of vegetable)
'standard crop' is the wordplay.
'standard' becomes 'par' (standard of play in golf).
'crop' becomes 'snip' (synonyms).
'par'+'snip'='PARSNIP'
'providing' acts as a link.
(Other definitions for parsnip that I've seen before include "Type of root veg" , "Spar pin (anag) - vegetable" , "Pale carrot-like vegetable" , "Tapering vegetable" , "Pips ran oddly through the vegetable" .)