Micrantha is just a species name.......Heuchera micrantha, aka western or small flowered alum root. There are numerous cultivars of this species, 'Palace Purple' being just one.

Would not expect these to hold up well in Southern heat and humidity.

good to know, that was going to be my next question. you always have to question these big box stores.

"you always have to question these big box stores."

That's because they are not plant nurseries and are not plant focused. They just sell whatever plants their suppliers provide to them, whether they are regionally appropriate or not.