This is a new plant to me, so I know little to nothing about it, beyond what I've found online. It's very interesting, however! I'm going to keep my eye out for one, because I'd certainly like to have one in my collection!
Although it may be a trait of all the
Adenium, as near as I've been able to learn,
Adenium obesum is the one that has the especially thickened trunk. (From the article I've cited here, scientists aren't certain if there actually are more species in this group, beyond
Adenium obesum).
A site with seemingly good information is this one from the University of Wisconsin:
https://www.hort.wisc.edu/mastergardener/features/indoor-tenderplants/desert%20rose/adenium.htm