Hickory tree (5)
I believe the answer is:
'hickory tree' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pecan that I've seen before include "Type of nut" , "Smooth pinkish-brown nut, nice in pie" , "Nut tree of the southern United States and Mexico" , "Oval nut of south central United States" , "US nut tree" .)