Schlumbergera

Genus boundaries and stem structure

Plants of the World Online accepts seven species of Schlumbergera. The genus is native to southeastern Brazil. The checklist retains Rhipsalidopsis as a separate genus containing the Easter cacti R. gaertneri and R. rosea. The generic names Zygocactus and Epiphyllanthus remain synonyms of Schlumbergera [2-WWW].

The stem consists of successive short segments with determinate growth. Branching is acrotonic, meaning that new branches arise mainly near the ends of earlier segments. Segments may be flattened or angular. This arrangement distinguishes them from many elongated stems of Lepismium, where branches also arise along the middle portions of the axis. Comparisons within Schlumbergera also use flower symmetry, floral tube length and segment shape [Calvente et al. 2011].

DNA and changing genus boundaries

Calvente and colleagues compared three plastid DNA regions and the nuclear ITS region in 35 species of the tribe Rhipsalideae. The results showed that the broad genus Hatiora used at the time included separate evolutionary lineages. In 2011, the authors proposed placing its subgenus Rhipsalidopsis within a broader Schlumbergera. This historical treatment explains the names Schlumbergera gaertneri and S. rosea in the literature. The present atlas follows POWO in recognising the two genera separately [Calvente et al. 2011] [2-WWW].

Comparing traits with the relationship tree revealed repeated changes in flower symmetry. Bilaterally symmetrical flowers, with a single plane of symmetry, occurred in different lineages. Details of the reconstructed transitions depended on the analytical method. A single floral character therefore has limited value as an independent basis for genus boundaries. The study combined molecular evidence with stem and flower structure [Calvente et al. 2011].

Cultivar differences in flower longevity

Scott and colleagues observed five Schlumbergera cultivars in a chamber at 20 ± 1°C, relative humidity of 75 ± 5% and a twelve-hour photoperiod. They assessed 10 flowers per cultivar on at least four plants. Mean time from flower opening to the onset of senescence ranged from 4.3 to 6.2 days. This range describes individual flowers in a controlled environment, while the flowering period of a whole plant also depends on the succession of opening buds [Scott et al. 1994].

Two of the forms studied, ‘88-50’ and ‘88-68’, came from a cross between S. truncata ‘Rocket’ and S. × buckleyi ‘Buckleyi’. The parentage of the other cultivars was unknown. The comparison therefore concerns horticultural material with differing origins. Retaining the cultivar name when recording flowering allows a much more precise comparison of results than the common name Christmas cactus alone [Scott et al. 1994].

Regeneration from tissues

Somatic embryos were obtained from callus, tissue multiplied under laboratory conditions, in S. truncata ‘Russian Dancer’. They had their own shoot and root poles, distinguishing them from individual adventitious shoots. Embryo formation depended on the previous culture history and the sequence of growth media. The S. truncata card describes the experiment in detail [Al-Ramamneh et al. 2006b].

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