[3.P] The Summoner's Handbook: A Guide to the Pathfinder Summoner

[Cieyrin]

Is it possible to stack the Reach evolution to have a single natural attack with ridiculous range?

Unless otherwise noted, each evolution can only be selected once.

Unfortunately, Reach does not have any text saying it can be taken more than once or once per natural attack. It appears you can take it once and only once. Choose that natural attack carefully...