Hybridization
All taxa of the genus Schlumbergera flower uniformly purple except S. lutea, which is yellow flowering. S. truncata is also an exception. Plants with orange-red, pink, red, purple and even white flowers can be found in the natural habitat. Soon after the introduction of this species in 1818, the first crosses and selections were carried out and around the middle of the 19th century a considerable number of cultivated varieties already existed. In 1839, Schlumbergera russelliana arrived in Europe and was soon used for breeding by Wilbraham Buckley. The crosses Schlumbergera russelliana × S. truncata were then described by Moore in 1852 as Epiphyllum buckleyi. Today they are known as Schlumbergera × buckleyi or generally as ‘Christmas cacti’ and became very popular in England especially during the Victorian period.
With the beginning of the 20th century, the interest in the Schlumbergera hybrids ended. After 1960, individual breeders began to deal with hybridization again, for example Alfred Gräser in Germany and Joyce Carr in Australia with her ‘Liberty Series’ from the 1980s onwards. From around 1980, large nurseries became particularly involved and endeavored to breed strong and upright plants with new flower colors and shapes, instead of naturally hanging plants. In the USA, these were mainly B.L. Cobia Inc. in Winter Garden (Orlando, Florida). Their breeding concept was hybrids with polyploid (multiple), up to eightfold chromosome sets, with which they achieved some spectacular breeds. These were then patented and marketed in the 1980s as the ‘Cobia Collector Series’. This included the first yellow-flowering S. truncata variety ‘Gold Charm’. Schlumbergera finally also became interesting to commercial horticulture. Today, millions of small flowering plants of S. truncata hybrids and selections are sold in the USA for Thanksgiving in particular, and they are also sold in large quantities in Europe in late autumn and around Christmas. In order to meet this huge demand, several large nurseries have specialized in production. These are primarily de Vries in Netherlands and Rohde, Thoruplund and above all Madsen in Denmark. Today, S. truncata hybrids and selections have become an indispensable part of the range of plants offered by garden centers and nurseries.
The discovery of Schlumbergera orssichiana and the use of this species as a crossing partner increased the variability of the hybrids enormously. The first crosses S. orssichiana × S. truncata were carried out in Brazil by Countess Beatrix Orssich from Teresópolis, Brazil , who called her breeds ‘Queens’, which is why these crosses were given the Nothospecies name S. × reginae. Other breeders of these varieties in the 1980s were A.J.S. McMillan in England and especially Dolly Kölli in the USA. S. × reginae cultivars have never achieved the economic importance of the S. truncata varieties described above, despite their impressive flowers.
Schlumbergera opuntioides, S. kautskyi and S. microsphaerica, on the other hand, play only a minor role as cross partners. The latter two species are self-fertile and therefore crosses are rarely successful. S. lutea plays no role in hybridization. So far, the following interspecific hybrids have been given Nothospecies names, which can also be used when crossing in the opposite direction:
Schlumbergera × buckleyi = S. russelliana × S. truncata
Schlumbergera × eprica = S. orssichiana × S. russelliana
Schlumbergera × exotica = S. truncata × S. opuntioides
Schlumbergera × reginae = S. truncata × S. orssichiana
While Schlumbergera hybrids and selections exist in large numbers, the hybridization of Rhipsalidopsis began quite late and the number of cultivars has remained significantly lower. This may be partly due to the fact that there are only two initial species available, R. gaertneri and R. rosea, whose natural forms are also quite uniform in color, in contrast to the range of color variations of Schlumbergera truncata. Rhipsalidopsis cannot be hybridized with Schlumbergera under natural conditions.
It was Alfred Gräser from Nuremberg who first crossed R. gaertneri and R. rosea in 1932. This hybrid was described by Werdermann as Rhipsalis × graeseri in 1939 (Kakteenkunde 1939: 10) and was recombined by Moran to Rhipsalidopsis × graeseri in 1953. The name R. × graeseri applies to crosses in both directions, i.e. no matter, which plant is mother plant or pollen dispenser. In the 1960s, it was Harry Johnson of Johnson Cactus Gardens in California who bred some famous varieties, such as ‘Crimson Giant’ or ‘China Pink’.
B.L. Cobia was also involved in hybridizing Rhipsalidopsis in addition to breeding Schlumbergera cultivars. In England Abbey Brook Nurseries produced some notable Rhipsalidopsis varieties (e.g. ‘Easter Wedding’), as well as Japanese breeders (e.g. the two-colored ‘Parnell’). Special mention should be made of Andrew Savio in Australia, who succeeded (probably by induced mutation) in breeding varieties with double flowers, e.g. his famous ‘New Double’.
In the ‘fairway’ of the winter-flowering Schlumbergera hybrids, the Rhipsalidopsis varieties very quickly gained popularity as spring bloomers or ‘Easter cacti’ and are today produced in masses and parallel to the Schlumbergera varieties by the aforementioned European nurseries de Vries, Rohde, Thoruplund and Madsen. Today there are Rhipsalidopsis varieties available flowering in white, orange, pink, red, purple, dual colors and variations with darker or lighter central stripes. Yellow is the only missing hue. The plants also have to grow vigorously and upright so that, just like the new Schlumbergera varieties, they do not have to be cultivated in hanging baskets.
Mass production makes the new Schlumbergera and Rhipsalidopsis varieties affordable, but in most cases, they are ‘disposed of’ by the ‘consumer’ after flowering and not further cultivated. For the gardener it is no longer worthwhile to sell the plants with labels and variety names. Thus, even the most beautiful new cultivars disappear into anonymity. May this register help to get the plants out of their namelessness and give them the place in our collections that they deserve!