My guess was that it was going to be the container library, rather than the language itself. If libraries are included, then Clojure-inspired HAMTs are in Haskell as well. But really, Clojure, Haskell and Scala are all just implementing Bagwell's ideas, http://lampwww.epfl.ch/papers/idealhashtrees.pdf whose feasibility was shown in Clojure.
However, your graph will be much more complicated if libraries are allowed to influence each other, rather than strictly considering language features.
> My guess was that it was going to be the
> container library, rather than the language itself.
This walks a thin line for sure and in Scala the line is almost microscopic. I'll keep it for now since my reasoning was the same as the Erlang->Scala influence. A core language library that is rarely viewed as other than a core feature.
See e.g. for Haskell, originally as http://www.haskell.org/pipermail/haskell-cafe/2010-February/... and now as http://www.haskell.org/wikiupload/6/65/HIW2011-Talk-Tibell.p...
However, your graph will be much more complicated if libraries are allowed to influence each other, rather than strictly considering language features.