Orchids that Attack

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How many growers know of an orchid that attacks? There is one, well quite a few in fact! Give up. Here’s a hint. It can fire its pollinarium up to about a metre, but usually just attacks unfortunate bees. Any idea? Well, it’s orchids in the genus Catasetum (pronounced kat-uh-SEE-tum). This orchid is famous for attacking insects with its pollen. I don’t know of any other orchid genus which actually attack insects. Many other deceive insects into mating with the flower, some contain hinges which swing insects into contact with the pollinarium and some even close their labellum trapping the insect inside for a short time, but the Catasetum actually goes one better and actively attacks insects.

There are between 50 and 150 species in this strange genus, depending on which expert you believe. This genus is not commonly grown in Brisbane, but you see a few examples of these orchids at the shows. They are fairly easy to grow in conditions similar to Cattleyas, although as usual, you should research each individual species as conditions do vary between species. This genus is deciduous in that they drop their leaves and remain dormant throughout winter. As with any deciduous orchid, they should be kept quite dry during the dormant period.

Catasetums are a bit of an anomaly in the orchid world for a couple of reasons. Firstly, there are male and female flowers. A Catasetum can produce male or female flowers, but usually have all flowers of the one sex in a flowering. Occasionally you will get hermaphroditic (bisexual) flowers mixed in with the normal single sex flowers. The male flowers are the larger more showy flowers, while the female flowers are smaller and much less showy. In addition, the female flower lips are always nonresupinate (held uppermost) while the male flowers are almost always lowermost, as with most orchids. Surprising, female flowers are very similar in all Catasetum species, while the male flowers show large variation across the various Catasetum species. Female flowers tend to occur when the orchid has very high light levels, while the male flowers tend to develop in lower levels of light. As the male flowers are much more desirable, growers tend to reduce the light levels during the formation of flowers to ensure male flowers are produced.

The second, even more striking aspect of Catasetums, is that they explosively attack insects. Catasetums have developed an amazing system of pollination using insects to carry the pollen from the male flower to the female flower on another orchid plant. The male and female orchid flower produces fragrances extremely attractive to a particular type of insect, usually a specific bee, and always a male bee. Each Catasetum species has adapted to suit a particular insect and no other.

Ctsm. Bound for Glory

A typical male Catasetum flower, Catasetum Bound for Glory. Different species of Catasetum show great variation in the male flowers.

Typical Female Catasetum

A typical female flower with the lip uppermost. Female flowers of all Catasetum species are similar to this.

Intact Column

Here, you can see a close up of an intact male flower. You can see the column with the pointed anther cap at its apex. You can also see the "antennae" near the base of the column. This is the trigger to release the pollinarium from the column. The pollinarium is held under the anther cap sprung tightly. When the insect touches the "antennae", the pollinarium is released with great force and a sticky disc on one end secures it to the back of the insect. The explosive force of the release and subsequent impact on the insects back is such that the terrified insect leaves immediately and will never return to a male flower, a case of once bitten, twice shy.

Column after anther fired

Here is the column after the anther cap has been fired.

Note the right hand "antennae" is fairly straight, while the left "antennae" curves across under the right "antennae". The "antennae" may be straight or curved, but curved "antennae" are not functional. In this example, only the straight right hand "antennae" can fire the pollinarium.

Fired Anther

Here is the anther and pollinarium after being fired. The sticky disk is stuck to lip of the flower.

In this case, the "antennae" was triggered by an unsuspecting photographer attempting to straighten the left hand "antennae" before photographing the flower. The result caused a bit of confusion, as I was positive the lip did not have that protrusion a minute ago.

Even though an insect has been attacked in a male flower, the attraction of the flower fragrance will however, attract it to the female flower, as it is totally different in appearance to the male flower. The female flower is constructed with the lip uppermost such that the insect visiting the flower must enter upside down placing the pollinarium in the correct position on the stigmatic cavity. The stigmatic cavity is extremely sticky, so when the insect backs out from the flower (which it must do due to the small size of the female flower), the pollinarium breaks from its sticky disk securing it to the insect and is left in the stigmatic cavity. This completes the pollination cycle.

That pollination ever occurs is a miracle. An insect of exactly the correct size must visit the male flower, position itself in the correct position and trigger the pollinarium which must land and stick in exactly the correct position such that the insect can still fly and also be in the correct position to pollinate the female flower. The insect must then fly off to locate and visit a female flower in the next couple of days. The insect must enter the flower in the correct upside down position and deposit the pollinarium in the correct position on exit. If all this occurs correctly, the pollination is completed, a seedpod will form, ripen, disperse the seed which hopefully lands on suitable locations such that some new Catasetums will grow.

The chance of all this going to plan must be extremely low, but as is evident by the existence of Catasetum species, must occur regularly. Makes you think, doesn’t it. Anyone feel like buying a Golden Casket ticket now?

Graham Corbin

 

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