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Disocactus amazonicus and questions
One flowering cactus I’ve found to be a delight is Disocactus amazonicus (also known as Wittia amazonica and Wittia panamensis). It has a blue purple colour on the petal tips.
I tried crossing it with the epiphyllums that we grow. These are usually open for about three days. I have had absolutely no success. Observing the flowering time with this plant, I found that the flowers opened late at night and were still open in the morning until they closed up by, or before mid day. So they were open for about 10–12 hours. Who else has had experience with this plant? Few people in New Zealand grow this species. What I found interesting was, that although the time of day the flowers were open was different from the time of day the nocturnal flowers were open, like them, D. amazonicus opened for less than twelve hours. As a result, I wondered if it would hybridise with other twelve-hour flowering plants, such as certain epiphyllum, selenicereus or hylocereus species. Another feature of this plant is that it sometimes sets fruit, as do some rhipsalis species.
I wonder if others have found that this plant’s flowers are open for a different length of time. The reason I ask this is that, from my reading, some information on the flowering time of another plant seems so different from what I’ve seen or experienced. Many references to Epiphyllum anguliger I have seen, have stated that the flowers are night blooming. One reference was the Rainbow Gardens plant catalogue and another, Ted Anderson’s book ‘The Cactus Family’ (2001), where E. anguliger is referred to as ‘Moon Cactus’ and ‘Queen of the Night’. Maybe my species of this ‘rick rack’ cactus is different? This is something I would not have expected. The flowers of E. anguliger last (for me), for three days and not overnight as this other literature suggests. 
I do know that when the flower is pollinated, it tends to collapse and die sooner, because the flower’s life is complete. Another reason (or factor) why the flower won’t last long is that, when a plant is under water stress and the flower is unable to conserve water, it closes sooner to help reduce water loss in the plant. I have found that E. crenatum, and a number of other epiphytic cacti species, last about three plus days (depending on the weather and if the flower is pollinated).
With the epiphyllum genus, there are two distinct flowering time lengths; night (nocturnal) flowering for twelve hours and three day flowering times. The three day flowering disocactus (this now includes aporocactus, nopalxochia, heliocereus, chiapasia) and epiphyllum seem to interbreed freely. The twelve-hour epiphyllum flowerers do not cross with the three-day flowerers.
The classification of epiphytic cacti makes me wonder if this group could be better ‘sorted’ by considering other key factors. I expect that most species of epiphytic cacti have been found, so if we look at the genetic factors of these plants, we could look at how we group them. This leads me to ask questions.
Question 1 Maybe one of the first features to divide these groups of epiphyllums, disocactus and pseudorhipsalis etc, could be done by flowering time. One group open for twelve-hours, the other group open for three days. Nocturnal may not be the best term to use if D. amazonicus is placed in this group.
Question 2 Of the three day flowerers, which ones are genetically compatible or incompatible? Already we know the ones that do and do not hybridise, by our resulting epicacti or epiphyllum hybrids.
Question 3 Of the twelve-hour flowering types, which ones are compatible or incompatible and what makes them so? Would D. amazonicus fit more comfortably into another group other than disocactus?
If one is to look at the past, we find that in the 1820s, Disocactus speciosus, (Syn. Heliocereus speciosus) 
and D. phyllanthoides (Nopalxochia phyllanthoides) were crossed. The first recorded hybrid of these epiphytic cacti. These two species are very different. One species has many sharp spines, and big bright red open flowers, with stems of up to five sides. It has spines on the flower stem as well. The other species, Disocactus phyllanthoides, is spineless, has comparatively closed, soft pink flowers and two sided stems. On viewing these plants (D. speciosus and D. phyllanthoides), they seem so different because of their form. If someone hadn’t tried crossing these two plants, we wouldn’t have the knowledge we have now. Then these plants would not have been classified, as in Ted Anderson’s book, into the same genus.(Disocactus)
So genetic compatibility has been used in gauging if these plants belong in the same genus. Maybe, because of the distinct differences between D. speciosus and D. phyllanthoides, we need to look at the genetic characteristics of these plants instead of only their physical characteristics.
