Purple petioles?

Google was not particularly helpful unless you are smoking that native.

The purple-toned structure would probably just be called the 'base' or 'bottom' of the petiole. Likely botanists have an esoteric name for that specific slightly widened portion. But I don't have a clue what it might be called.

"Google was not particularly helpful unless you are smoking that native."

LOL!

What's interesting is I've got two Fringe Trees (C. virginicus) planted side-by-side, but only one displays this feature, and it's prominent. They were grown by same wholesaler and planted at same time. This native is not indigenous here, so it may be something that is normal and common of the species. Hopefully someone who lives in its native range and sees it on a regular basis can clarify.

Not sure this qualifies as a stipule, but that is usually the term for a leaf-like structure at located at the base of the people.

No stipules there that I can see.

They came from Bailey's and I'd like to say they were seed grown, but I'm not sure of that.

'Emerald Knight' Fringetree is described as having "... young stems (that) are a shiny dark burgundy". http://www.boldspring.com/trees/che-lb

Mmm, sounds like someone has already selected for this trait. It is far superior to the othe seedling I have in just about every characteristic that plants are evaluated for garden merit. The big question now is will it produce fruit? The fall color is an incredible scarlet that lasts about a month. No, I'm of couse kidding.

Seen this on the most vigorous sprouts on my fringe trees. There's alot of sprouts because the EAB keeps killing them back.