It's more accurate to say that
Black cumin is a spice from the same family as Nigella. I don't think the regular grocery store cumin is the same (Cuminum cyminum). Whole seeds are unmistakeably different. Ground Black cumin is black. The ground cumin in my cupboard is golden-brown. The two species (Nigella nad Cuminum) smell very similar, but are not at all related, and the the two plants also look very different.
Cumin seeds look like fennel seed (closely related) on the left, and Nigella sativa look similar to Nigella hispanica on the right. Photos of seeds of the actual species are readily available on the web. Even wikipedia has correct images:
http://en.wikipedia.org/wiki/N...
http://en.wikipedia.org/wiki/C...
