Good Morning Bob, 

Thank you for contacting the U of M Extension Service. 

Please click on the following link: tps://mdc.mo.gov/discover-nature/field-guide/butternut

Butternut trees are in the same family as walnuts. Butternut is called the "white" walnut. You did not indicate how old the trees are. Are you sure of their identification? 

Here is another link to the MN DNR: https://www.dnr.state.mn.us/trees/butternut.html

And another link to the Arbor Day Foundation: https://arbordayblog.org/treeoftheweek/the-butternut-tree/

I would suggest as the tree leaf out and produce their blooms, that you use some of the above research to ensure you have butternut trees. 

I have also attached a very detailed document from Perdue University about butternuts and a detailed nut identification guide. 

Good Luck!

Good Morning Bob, 

I agree possible subspecies or maybe they cross pollinated since they are in the same family. 

Glad your trees are healthy and happy in this climate! 

Good Luck!

Good Morning Bob, 

I don't know if they can cross pollinate. I am just speculating. 

I have also planted trees from the Arbor Day Foundation. They come as bare root small sticks. Again, I'd watch them closely as they leaf out and bloom in the spring. Maybe the above research will help to specifically identify them. 

Good Luck!