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Pollination of the Slipper Orchids

Paphiopedilum, Phragmipedium, Cypripedium, and Mexipedium

Text and Photos by Marianna Max


Even for people who have gained experience pollinating other orchid genera, Paphiopedilum and Phragmipedium pollination can be quite mystifying at first glance. For those used to seeing a small sticky stigma that seems to "grab" the pollen, the broad smooth stigma found in Paphiopedilum and Phragmipedium can seem quite foreign. Pollination of the subfamily Cypripedioideae (Paphiopedilum, Phragmipedium, Cypripedium, Mexipedium) is in fact quite easily accomplished once all of the "parts" are recognized. For that reason we will start with an anatomy lesson and dissection of a typical Paphiopedilum flower. Figure 1 shows the front view of an intact Paphiopedilum. In this first view none of the sexual parts of the plant are visible. The stigma (the female part of the plant which is the gateway to the ovary) is hidden within the pouch at the back of the column (the central extension of the stem and ovary that gives rise to the anthers, stigma and staminode). The anthers (there are two separate anthers in cypripedioids, unlike other genera which only have one anther) are hidden behind the ears of the staminode. The staminode is an interesting structure which no doubt helps to attract the pollinator to the flower and which provides part of the mechanical barrier that directs the pollinator in the right direction to pick up and deposit the pollen on the stigma.

Figure 1
Figure 1: Front view of Paphiopedilum

In Figure 2 we see a side image of an intact flower. For the first time we can begin to see the sexual parts of the flower. Behind the staminode we can just see a bit of the anther. The majority of the stigma is hidden behind the side lobe of the lip. We can just see the back of the stigma where it attaches to the column.

Figure 2
Figure 2: Side view of Paphiopedilum

In Figure 3 we have removed the pouch where it connects to the column and view the flower from the bottom. For the first time we can clearly see the stigma, a broad, smooth, flattened fingertip-like structure. While it is possible to pollinate a Paphiopedilum or Phragmipedium without removing the pouch, it is considerably easier to see what you are doing if the pouch is removed. Generally an easy way to remove the pouch is to rock it to one side until you hear a crack and then to the other side. This should partially detach the pouch at each side and the rest of the removal can easily be accomplished with a bit of twisting and pulling. Be sure and support the rest of the flower with your other hand so as not to damage it during this process. Alternately, the pouch can be removed by cutting with small scissors but if you choose this route be sure and sterilize them so as not to risk transmission of virus. There is no need to remove the synsepal since it can generally be bent back out of the way of the stigma (In Cypripedioideae the synsepal is formed by fusion of the two lateral sepals and it forms a sort of apron behind the pouch).

Figure 3
Figure 3: Paphiopedilum with pouch removed

Figure 4
Figure 4: Paphiopedilum column

Once the pouch is removed the hard work is really done. We will look at a few more views of the flower just to provide a thorough orientation, but at this point we have access to all of the structures we need to complete pollination. In Figure 4 we move in closer so as to see the anther and the pollen on one side of the column (remember that there is a second anther on the other side). You can also see the relationship of the anthers to the stigma and column in Figure 5. In this view we have turned the flower upside down and are looking at it from the front. The stigma can clearly be seen and the two anthers can barely be seen on either side of the column behind the stigma. The anther holds the pollen, which is attached via a small horn or "hanger" off the column. In paphiopedilums, the pollen is held in a waxy fairly undefined mass with the consistency of mealy beeswax. It is difficult to distinguish the anther cap (i.e. a cup-like structure that is well developed in other genera that holds the pollen) in paphiopedilums. At most, the anther cap in paphiopedilums appears to be a slightly more consolidated waxy surface that lies on the outermost region of the pollen mass. This modification can best be seen in the fourth image as the darker area of the pollen mass. While in most genera, the pollen can easily be separated from the anther cap, this is often difficult to accomplish in paphiopedilums.

Figure 5
Figure 5: Paphiopedilum with pouch removed, looking up

In Figure 6 we can see where the pollen mass has been removed from one of the anthers and an attempt has been made to separate the inner pollen mass from the anther cap. The pollen mass can be removed by grasping it with forceps or by sticking it to a toothpick. Since the pollen mass is not particularly sticky, it may be necessary to lick the toothpick or even to use the sharp end of the toothpick to impale the pollen mass should you choose to use a toothpick (for pollination). It probably is not necessary to remove the inner pollen mass from the anther cap to achieve pollination since both are soft and waxy and can easily be smeared onto the stigma.

Figure 6
Figure 6: Paphiopedilum pollen

In Figure 7 we can see where the inner pollen mass has been applied to the stigma. This can be accomplished by "sticking" the pollen mass to the stigma using a bit of the saliva left on your toothpick or by simply by pressing it up against the stigma surface using gentle pressure from the toothpick. If the inner pollen mass is not removed from the anther cap before applying to the stigma surface, try to position the anther cap/pollen mass so that the inner pollen mass surface is against the stigma. The pollen masses from both sides should be used to maximize the amount of seed obtained unless one of the pollen masses is needed for other pollinations. The final step in pollination is to the smear the pollen mass over the surface of the stigma. This can best be accomplished with the flat end of the toothpick. Gently push the pollen mass flat and spread it over the surface of the stigma much like you would butter a slice of bread. Be gentle so as not to gouge the stigma or inadvertently break it off.

Figure 7
Figure 7: Pollen applied to Stigma

Cross pollination is always preferable for reasons of genetic diversity, but paphiopedilums and phragmipediums can often be self pollinated successfully if a suitable outcross is not possible. The visible response to pollination in paphiopedilums is minimal and often it is difficult to tell if the pollination has taken until the ovary begins to swell. Unlike many other genera, the flower does not show any initial wilting in response to pollination but abruptly falls off the ovary leaving a clean scar at the ovary tip. The ovary does not swell right away but if the stem doesn't turn brown and desiccate it is likely that your pollination has been successful.

The final image, Figure 8, shows a view of the ovary several months following pollination. Note the lack of the wilted flower at the apex of the ovary, which is otherwise typically present in orchids outside of this subfamily.

Figure 8: Developing capsule of Paphiopedilum fowliei
Photo by Dale Borders


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