Don't let the term "ornamental" fool you in this case, these are edible hot peppers, just like any jalapeno or cayenne. It's just that they're so stunning that many people grow them to enjoy with their eyes and not with their mouths.
The Black Pearl is firmly in the medium hot pepper range, about 4 to 12 times hotter than a jalapeño. They ripen from green to black and finally to red.

It is characterized by distinctive black leaves and fruit. It was developed by Arboretum Floral and Nursery Plants Research Unit scientists Rob Griesbach and John Stommel of the agricultural research service’s vegetable laboratory