Look at this page
http://oregonstate.edu/dept/ldplants/2plants.htm#nyssa

Here is a link that might be useful: to ID Nyssa sylvatica

Looks similar to buckthorn. My black gums don't have thorns, must be a new defense system against the people that try to chew on the bark, trying to find the black gum within.

Looks kind of like Elaeagnus.

Black gum doesn't have thorns.

The leaves look similar, so one might understand how the mistake was made.

Cool. Thanks for the confirmation. I'll let you all know what they say it could be.

Looks to me like they sent you a Sideroxylon lanuginosum (fka Bumelia lanuginosa), common name being Gum Bumelia among others. The leaf emerging from the thorn in front of your thumb knuckle in the second picture seems very typical of the plant. I'd say you're lucky since it's an interesting tree and a hard one to find in commerce. And it is a Missouri native. Who DID send it to you?

Apparently "gum" was a basis for confusion at some point.

Got it from a place called Missouri Wildflowers Nursery. My wife ordered about a dozen items from them and turns out they ran out of the Nyssa Sylvatica I piggybacked on her order so they substituted this AND didn't charge us.

Guess they could have called to see if I wanted to substitute anything for the Nyssa, but a free plant isn't bad. She says they're nice enough on the phone and I'm happy with the quality of the plants they sent.

It's good to know what this is. I might stick it up in a row of mostly walnut trees. If it competes well it stands a chance!

Not fair to make gum bumelia go up against walnut (assuming black walnut) with their toxic juglone secretions! Bumelia's quite a lot smaller tree, too.

Thanks for the info on the nursery--I've looked at the Mo. Wildflowers website in the past but they don't advertise Gum Bumelia. For a while I was trying to get it from the Prairie & Wetland Center in Belton, Mo. but they were always out of stock, but finally got some from Sunshine in OK. I never know when I might need another Gum Bumelia.