The following article titled Moving Lablellums written by Helen Lawrence is reproduced from the NOSSA Journal Volume 36 (1) February 2012
Labellums are fascinating. Well I think they are fascinating, especially the ones that move.
Bunochilus viriosus with the labellum down
Why do these labellum move? You may have observed that the orchids which have labellums often have “hoods” and inside these “hoods” are the pollen. It is quite simple, the pollinator lands on the labellum, triggers it and is held captive by the labellum. As it struggles to free itself it pollinates the orchid. Clever, isn’t it?
Bunochilus viriosus with the labellum up
So that these labellums can capture the insect they need to be sensitive. Consequently they can easily be “set off.” This can happen with of a gust of wind, or if the plant is in a pot, the labellum may trigger if the plant is moved/knocked.
It is easy to see these labellums as they move up into their “triggered position.” They move reasonably quickly, so the insect does not have time to respond.
However, how does the labellum return to its “normal” position? Does it slowly return to the position, or does it happen in a sudden movement in the same manner as when it is triggered?
One day when I was travelling in the car with a Pterostylis curta (Blunt Greenhood), I observed something very interesting. When I looked at the flower, the labellum was up, but then when I looked at it a minute or two later, the labellum was down. The labellum had to move quickly. However was it the bumps in the road which caused it to move? I had to find out.
I devised an experiment to satisfy my curiosity, and find out what these fascinating labellums actually do.
First I had to find an orchid with a labellum that could be triggered. I ended up using an Oligochaetochhilus bisetus (Two-bristle Greenhood).
Second I had found a good camera that could take high definition video. I placed it on a “tripod” (a pile of books).
So I had set up my apparatus, set the camera rolling, triggered the labellum, and left the room.
So what happened?
For the first six minutes after I had triggered the flowers nothing happened. There was no movement that I could see.
In the next five minutes, the labellums of the two flowers slowly moved downwards until they were half way down.
After twelve minutes of the flower being triggered, the labellum returned rapidly to its original position. This final stage of the labellum moving lasted for less than five seconds, and appeared to move at the same speed as when it was triggered.
So it looks like the labellum returns to it normal position first moving slowly and then in a rapid final movement which returns the labellum to its original position.
If I thought it would be that simple, I was mistaken.
As I briefly looked through the fifty minute video I took, I came upon something that made no sense to me.
A minute after the labellum had returned to its resting position, one of the labellums suddenly returned to its “triggered” position. What’s more, there was nothing in the room to trigger the labellum: no wind, no insects, and no people. So what triggered the flower?
I do not know. Six minutes after the labellum was triggered it returned to its original position, and then two minutes later the other flower’s labellum moved into the triggered position. The first flower was triggered again for no apparent reason at all, four minutes after the second flower was triggered and still remained up.
Once the labellums returned to their original position, there was no more movement.
Maybe triggering the labellum causes a chain reaction. Maybe the labellums periodically “trigger themselves.” Well, I can’t give you any answers, all I can tell you is that it looks like this is an example of how we barely know anything about these wild gems. They are beautiful but bizarre and of course fascinating!
After 7 minutes, just before the labellum moved
After 12 minutes, labellum about to fall
After 13 minutes, labellum in original position
As a 50 minute video is a bit long to watch, Helen has produced a four minute video, so watch and enjoy the music!