Thanks for this article.. I enjoyed reading it. I have long shared your fascination with the relationships between plants that are botanically close to each other, but look nothing alike. One example came in an unpleasant way.. my Mom had a terrible skin reaction last year that was diagnosed as poison ivy. Only problem with that was she had not been exposed to any poison ivy in many years. There is none in her condo garden. But she had eaten a lot of mangoes and cashew nuts and it turns out both are related to poison ivy. The dermatologist told her that once you've had a poison ivy reaction you should not eat mangoes or cashew nuts ! She was very unhappy as both were favourites of hers.
I had quite a surprise when I saw the picture of your Disocactus. As it happens, I've had a Disocactus Ramulosus for awhile and I guess I missed it when they changed the family names, yet again ! I too, wish that botanists could agree and quit changing names on us all the time :-). It seems Ramulosus is now lumped in with what I've always known as Flagelliformis, aka Rattail cacti. When I saw that picture in this article I had to go look mine up to be sure I had the proper name for it, because they couldn't possibly look less alike if they tried ! Ramulosus looks very much like an Epiphyllum, or orchid cactus, nothing at all like the pictured Disocactus. I haven't yet seen mine in flower but I know they're very similar to Rhipsalis flowers and the berries that come afterward are very like what you get on many Rhipsalis, and indeed, Disocactus ramulosus was, at one time, called Psuedorhipsalis ramulosus.
I used to wonder why botanists use flower characteristics to compare plants, because there are only five basic flower forms. But along the way I've learned there are seemingly endless, often minute, differences in the way that flowers are constructed internally, many of which are not at all obvious to the casual observer. And now that DNA testing is available, there have been some really interesting discoveries about some plant relationships made by researchers, but the testing is very expensive and time consuming so it's going to be a very long time before we get DNA studies on many plants. For now, most will concentrate on those with the highest commercial value. Meantime we plant enthusiasts will just have to try and keep up with all the botanical twists and turns as botanists shuffle plants from one family to another, based on their studies and interpretations of the findings. And continue to scratch our heads when it turns out that two plants we thought could not possibly be related in any way are in fact, kissing cousins :-).