Purple-tipped Acropora sp. (variety: "Larry Jackson's Purple Tipped Monster")
This Acropora species is an extremely fast grower (see photo series documenting growth). Along with Montipora digitata, this Acropora is probably the fastest-growing small-polyped stony coral in our aquaria.
Polyps are quite small, each situated atop a small raised bump on the branch, and are mostly retracted during the day.