From the NHLA:
"A National Hardwood Lumber Association Inspector will not make any distinction in species between Hickory and Pecan."
http://www.natlhardwood.org/pdf/Rulebook.pdf Go to page 29.
This is because you can't tell the difference between the two. Yes, I can tell the difference in the trees. Yes, I can tell the difference in the logs. No, I can't tell the difference in the lumber.
I have actually been involved in a "Yes, I can....No, you can't arguement." This was years ago. So, I named the logs correctly and then they were marked from the ends and sawn. Presented to me as lumber, mixed together. I lost the arguement.