Rhipsalidopsis gaertneri

Name and identification

The name currently accepted by POWO is Rhipsalidopsis gaertneri (Regel) Linding. In that database, Hatiora gaertneri and Schlumbergera gaertneri refer to the same species. Its native range is southern Brazil, where it is associated with the wet tropical biome. This identity is retained when discussing research published under Hatiora gaertneri [2-WWW].

The stems are jointed and branch near the ends of earlier segments. Flowers are radially symmetrical with a short, inconspicuous tube. These features distinguish them from the elongated, bilaterally symmetrical flower of Schlumbergera truncata. DNA research demonstrated the relationship between the groups, although their current generic names remain separate. In cultivation, the species is also a parent of the hybrid R. × graeseri [Calvente et al. 2011] [Boyle 2005] [2-WWW].

An extended period for successful pollination

Boyle studied vegetatively propagated ‘Crimson Giant’ plants at 20°C, relative humidity of 65 ± 5% and a twelve-hour photoperiod. Flowers lasted an average of 10.5 days. Successive groups were pollinated once with fresh pollen from compatible genotypes, from the day of opening through day eleven. Fruit set remained at least 84% throughout that interval. The highest mean number of viable seeds per pollinated flower, 155, followed pollination on day four [Boyle 2005].

Seed numbers declined after day seven despite the continuing high frequency of fruit set. Counting fruits and viable seeds separately thus revealed two different effects of ageing. In an additional group of 17 flowers pollinated after senescence symptoms had appeared, 35% set fruit. Perianth condition and the pistil's reproductive capacity therefore changed at different rates. This result concerns ‘Crimson Giant’ under chamber conditions and does not establish an identical pollination schedule for all Easter cacti [Boyle 2005].

The pollen pathway to the ovules

After pollen is received by the stigma, pollen tubes grow through the style towards the ovary. In the experiment, ‘Crimson Giant’ styles averaged about 24 mm. By removing them at successive intervals after pollination, the researcher determined when pollen had progressed far enough to permit subsequent seed development. Half the maximum yield was reached after approximately 26 hours. The comparison cultivar ‘Eva’ of S. truncata had a much longer style and required about 44 hours to reach the same relative level [Boyle 2005].

Pollen tube growth rate calculated from style length and response time was an indirect estimate. The experiment relied on final seed yield, supplemented by microscopic observations. For controlled crossing, a record of flower opening can be combined with the time compatible pollen was applied and the eventual number of viable seeds. Fruit formation alone describes only part of reproductive success [Boyle 2005].

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