On a previous entry here I wrote about how to get your Christmas Cactus to flower and on my other blog I wrote an entry on rooting Christmas Cactus cuttings. In the first entry here I alluded to something being fishy in regards to calling my plants "Christmas Cacti." Most of the plants sold today as "Christmas Cactus" are actually not the true Christmas cactus. These are not your grandma's Christmas cactus.
The Schlumbergera truncata cultivars being sold today as "Christmas Cactus" are actually the plant commonly referred to as "Thanksgiving Cactus." The real Christmas cactus is Schlumbergera x. buckleyi and is a cross between S. russelliana and S. truncata. The plant was produced by William Buckley at the Rollisson Nurseries in England.
Why are two different plants going by the same common name?
The reason that Schlumbergera truncata is going by "Christmas Cactus" today instead of "Thanksgiving Cactus" is because of money. Professional plant growers can get Schlumbergera truncata to flower easier and sooner. The ease with which they can be coaxed into blooming make them the more attractive of the two plants. Add to that fact that Schlumbergera truncata comes in a wider range of colors, Christmas is easier to market than Thanksgiving and you have yourself a Christmas miracle.
How to tell the two succulents apart.
Superficially the easiest way to tell whether you have a "Christmas Cactus" or a "Thanksgiving Cactus" is to look at the leaf segments. Look at the photo above of my Christmas cactus, that is really a Thanksgiving cactus, and notice the edges of the leaves. The Thanksgiving cactus has pointed edges that remind some people of crabs, where the real Christmas cactus has scalloped edges or no points on the leaves. Hybridizing has produced some plants with or without the pointed edges but the edge of the leaf is generally a good indicator. Also the way the plants grow help us identify the real Christmas cactus. Schlumbergera truncata (Thanksgiving cactus) grows more upright while Schlumbergera x. buckleyi has leaves and flowers that arch down.
If you're growing a Christmas cactus that was grown from cuttings which were taken from your grandmother's plant then the chances are really good that you do indeed have a "Christmas Cactus." Those of us not lucky enough to be growing heirloom plants and have plants grown commercially in the recent past are not so lucky. Christmas cacti can still be found in some places available for sale but they aren't as common as they were in years past. I've heard of cuttings of real Christmas cacti selling for a premium on places like ebay but I have yet to come across one in real life.
I won't even mention the "Easter Cactus" instead I'll direct you to a really good page that gives more information on this subject. Recognition and Culture of the Holiday Cacti (Thanksgiving, Christmas and Easter Cacti) by Paul J. Brunelle has illustrations of all three plants and good information.