I found somthing in Spung's "Corals Quick Reference Guide"
Montipora Digitata..(cabbage,lettuce,finger coral).. From the Red Sea Indo Pacific laggons,reef flats and protected upper reef slopes--Very shallow water strong light.
Purple morph-- .....encrusting or branching.... VERY light weight skeleton.....small polyps in depressions over colony surface.....simular to Porites corals
There is pic on page 31 Looks alot like what you have there! Says it's pretty hardy and non aggressive! I had some monti that grew like mad untill I had my big bleaching crash!
hope that helps! :D
sarah