We call them calla, although the true calla is a plant called Calla palustris, also known as bog arum. It's a hardy little plant native to our northern hemisphere that will grow happily in a pond or bog garden. The flower has a similar form to that of Zantedeschia, and they are in the same family, but of a different genus. In fact, Calla palustris is the only species in its genus, whereas the genus Zantedeschia comprises six species, all of which originate in the moist soil and swamps of southern and eastern Africa.
But that’s enough of the botanical language. We all know a calla when we see one, and calla is what we calla them. I don't get to many weddings, but I've yet to hear anyone exclaim, "Isn't she beautiful, and aren't the Zantedeschia rehmannia in her bouquet simply divine?" Maybe I attend the wrong weddings.
The other group is the Elliottiana. Callas in this group generally have green leaves covered with translucent white spots. I think this is probably what I have growing beside my pond. I'm only being vague because I've had them so long I can't remember where they came from. I probably had them given to me at least ten years ago. That's how callas proliferate. It's not that they're invasive.
On the contrary, they grow from tuberous rhizomes that tend to increase in size. Leave them in the ground over winter in this climate and they're goners, but dig them in fall for cool storage and come spring you can cut the big ones in half and pass them on to friends, as in — here, take this knobbly looking thing that looks like Mr. Potato Head's disowned cousin and stick it in your flowerbed. If the friend has never grown a calla, you'll hear the "Wows" a mile away when it blooms.
Between the hybridising and ongoing tissue culture of callas, the colour range keeps expanding. There are pinks, reds, peaches, and purples with names like Pink Chiffon, Pillow Talk, Bridal Bliss, and Garnet Glow. You can see that these are being marketed to the wedding planner rather than the gardener. There's also a black calla (read dark burgundy) called Black Forest. I suppose it's best suited to the "She should never have married him" wedding.