Arlene, I'd say your Thai giant is actually xanthosoma sagitifolia (sp)
It's a common mistake as the both get massive and the leaves look quite similair, they're often ever marketed as Thai giant.
I'd also wager that black magic is mismarked as well, black magic has velvety, matte leaves, and spreads by clumping, yours looks glossy, and with a pot that full, it looks like that one spreads by short runners, there's so many glossy leaf dark colocasia that I couldn't guess what it is...
A rose by any other name smells just as sweet!
