Juglandaceae is the family name that encompasses Walnuts, Hickory, Butternut, Heartnut, Pecans etc etc.
To ID many of the species its the leaflet count that narrows it down. You can then go onto leaf scars and shoot tip colouring etc.
There are however many crosses between the species, so permitations do exist, ie the Hican which is part pecan and part hickory, or the Paradox walnut which is a cross between American black walnut and English walnut, or the Buartnut which is a cross between Butternut and Heartnut etc etc
1 – Hickory Shellbark (Kingnut) or Carya laciniosa – nearly always 7 leaflets
2 – Hickory Shagbark or Carya laciniosa – 5 to 9 leaflets
3 – Pecan or Carya illinoinensis – 9 to 17 leaflets
4 – Walnut Black or Juglans Nigra – 11 to 23 leaflets with the terminal leaflet missing
5 – Walnut Common or Juglans Regia – 7 to 9 leaflets
6 – Butternut (White Walnut) or Juglans cinerea – resembles Black Walnut 11 to 17 leaflets but is has a terminal leaflet.
7 – Hickory Mockernut or Carya tomentosa – 7 to 9 leaflets
8 – Hickory Bitternut or Carya cordiformis – 5 to 11 leaflets
9 – Walnut Japanese or Juglans ailantifolia – 11 to 17 leaflets
Shell outlines and ridge furrowing is another method of narrowing down species.