Oh.. and HP-UX has never touched Svr4.. just saying.
Like AIX, as far as I know, both are Svr2 derivatives. While HP-UX did appear to have many things from the ill-fated Svr3, as far as I know, that really isn't the case.
Digital's Unix variants (there were multiple) are not shown... and they had great impact. DEC had a SVR variant, their Ultrix BSD variant and of course, one of the most successful deployments of of OSF/1 (all vendor variants not shown in the pic) which eventually became Digital Unix.
Mac OS/X isn't Unix at all and uses the (crummy) Mach kernel. Which, if you're going to show that, you might as well show all of the Mach based variants out there. And arguably if you're going to stray that far then QNX, etc... those types of things aren't out of the question.
Sigh.. this is actually a very hard thing to do. So.. IMHO, maybe just keep things to true Unix variants... even then the picture will still need some detail. But with OS/X, Linux, Minix and such removed, you'll have room for the missing things.
Also remember that for completeness, there are (very large) existing alternatives out there already as far as pictures go which do document the "Unix and Unix-like" OS's.
UNIX History
So.. pretty picture, but since it's not complete (nor accurate), people like myself and others will really pick this thing apart (don't put this into any textbook).