published in 10. Info-Letter of the IG Ascleps S. 18-20 (2003)
Asclepediaceae are interesting and bizarre plants. Personally, I find them truly beautiful indeed. Regrettably enough, it is impossible to procure seed restricted to this singular species and from only one habitat, simply by using mini brushes - in contrast to my husband's cacti. Therefore, one concern of asclepediaceae lovers should be to preserve the species in the collections through cuttings and seed. Yet unfortunately, there are no pollinators available in our part of the world.
In spring 2002 I began developing my own method of harvesting the polliniarii - pollinating by hand using a binocular (16- to 32-fold). My first efforts using tweezers and various loops failed. In most cases, tweezers are too big for the tiny guiding rail; loops and clips demand too much patience from the human pollinator, as far as I am concerned - even a glass of fine red wine did not calm me down sufficiently. Thus, the only solution was gluing the translator to a needle. Despite my doubts, this works well provided the glue does not wet the pollinarii. In most cases, you can even use each pollinarium glued in place twice as it will break off right at the body of the pollinium, if it has been put into the correct position after threading the guiding rail.
With hand pollination, it is important to bear in mind that asclepediaceae frequently produce only low-grade or no seed at all through their own pollen. They are self-incompatible. All my "self-pollinations" failed, except for one Stapelia longipedicellata. After three pollinations, this plant developed one double horn and the seed was harvestable. So far, this seed has however not germinated. It may only be germinable to a very limited extent.
Table 1 gives a survey on the attempts and their outcome (from the tough beginning until today). 26 species from 8 genera were hand pollinated.
Table 1: Synopsis of pollination attempts so far (2003)
Genus Huernia has the simplest flower structure. It is very clear and guiding rails as well as pollinarii are big. But in most cases half the corolla has to be removed using a razor blade.
Stapelia has rather large flowers, yet the guiding rail is hidden in the funnel-shaped structure of the corona. Additionally, there is often nectar or a nectar-like substance to be found at the bottom of the funnel, which makes the threading difficult.
The same applies to the Caralluma. They provided good training situations, but I rarely got two clones from one genus – and they never ever bloomed at the same time. Currently, I am breeding a Caralluma socotrana, hoping that two grafted seedlings will eventually bloom at the same time this summer.
Hand pollination of Hoodia requires a steady hand and a good binocular. Yet, it is definitely worthwhile going to some trouble, since seed as well as plants are rarely on offer. So far, I managed to hand pollinate Hoodia officinalis and H. pedicellata.
Larrylechia is tiny and thus hard to handle. Here, it is crucial, which angle the threaded pollinium forms with the guiding rail. If the angle is right, threading is easily successful. Unfortunately, several pollinated flowers died off after 4-8 weeks, one plant bearing two ovules contracted an infection and rotted away within two days. This reduced the success rate considerably.
Orbea and Piaranthus both feature a clear flower structure so that hand pollination works out well with them.
Ceropegia and Brachystelma are the genera providing most problems, however, as all of them possess very small staminal columns and even smaller pollinarii. The latter are almost spherical. A tiny triangle needs to be threaded into the guiding rail, which hardly ever works, as the spherical structure of the pollinii blocks sight.
Asclepediaceae - Distinctive Features of Hand Pollination
Each genus requires another angle between pollinium and guiding rail. This applies to the angle seen from above from a vertical perspective as well as from a lateral perspective.
Successful threading alone still does not account for a positive outcome. Only when the translator breaks off, the pollinium has reached the correct position in the guiding rail.
Effective threading also does not grant any visible success at all. The plants tend to grow back undeveloped fruit (meaning slightly thickened pedicels tenaciously clinging to the plant) when they cease growing. This happened with my pollinations from August onwards. My few successful pollinations from spring sprouted quickly and developed fruit. Stapelia divaricata, Stapelia longipedicellata and Hoodia pedicellata have to be mentioned here.
If "self-pollination" were avoided by pollinating two clones, the success rates were much higher. Whenever possible, you should use material from the same habitat.
The longer the time span between pollination and growth phase, the more fruitifications get lost.
In the last two weeks though, Orbea variegata, Huernia laevis, Huernia keniensis var. keniensis, Stapila gettleffii and Larrylechia cactiforme developed ovules from the thickened pedicles. Only Piaranthus framesii, Larrylechia marlothii, Hoodia pedicellata and Hoodia officinalis keep me waiting. These plants have not yet displayed any signs of growth, as they have not yet finished their rest.
In the last weeks of autumn several spontaneous fruitifications turned up where I had not pollinated. This applied to Ceropegia Africana, Ceropegia woodii, Ceropegia stapeliiformis subsp. stapeliiformis and Ceropegia stapeliiformis subsp. serpentina, which may have pollinated each other, and Stapelia gigantea. When I controlled the Ceropegia flowers, I found a much higher rate of threaded pollinii. Self-incompatibility may play a major role here.