Illustrating language history
This image illustrates the situation that any researchers trying to understand and reconstruct the past of a current situation with related tokens faces - be it in biology, linguistics or another field. Only a sliver, a slice of time is available to us and from that we try to go back and reconstruct relationships.
What's nice about this picture is the branches reaching across (C), thus appearing close to others (B) in that slice of time, but actually it's genealogically related to another further away token (F). It does not really illustrate horizontal influence, i.e languages (in our case) becoming similar due to contact - unless you consider the closeness across the x & z-axis', like with C & B.
Also, notice the branches that don't make it all the way up, the extinct species/languages/etc.
I saw this image for the first time in a presentation by Fiona Jordan and liked it a lot. It's originally from Strickberger (1990), who adapted the illustration from Levin (1979). Thanks @ on twitter for the detective work in tracking that down!
I hope you also find it illustrative and inspirational.
Levin, D.A. (1979) Hybridization: An evolutionary perspective. Stroudsburg, PN: Dowden, Hutchinson & Ross
Strickberger, M.W. (1990): Evolution. Jones and Bartlett, Boston.