Orchids are unique in the floral world. Two distinctive characteristics that set orchids apart from other plants are the labellum and the column.
The labellum is a modified petal. It is extremely varied in appearance; “often lobed, spurred, adorned with glands, appendages of calli (callus, a hardened swelling or thickening of the skin), sometimes mobile and highly irritable and often brightly coloured”. * The labellum is important for pollination.
The column (as described by Bates and Weber) “is a distinctive feature of all orchids and a unique structure in the plant kingdom. It is formed by fusion of the male parts ‘stamens’ and female organ ‘pistil’.”*
Below are examples of the various types of labellums and columns in some South Australian terrestrial orchids. Each genus has its own characteristic labellum and column.
Thelymitra – though the labellum is almost indistinguishable from the other petals and sepals, the column is quite complex.Dipodium or Hyacinth OrchidPterostylis or Greenhoods – generally a simple labellum with the column hidden well back into the hood.Arachnorchis (syn Caladenia) can have quite varied and complex, mobile labellumsCorybas or Helmet Orchid – the labellum dominates and the column is hidden deep inside the flower.Diuris or Donkey Orchid – the labellum is divided giving the appearance of more than one structure.
This month’s entries are an interesting collection as it is probably the first time that all entries are currently in flower. Rosalie Lawrence entered a Pterostylis pedunculata, Ricky Egel (second) Corysanthes despectans, Robert Lawrence (third) Pyrorchis nigricans whilst both Rob Soergel and Claire Chesson (winner) entered Pheladenia deformis. All four are colony forming species.
Both parts of the scientific name for the winning orchid refer to the labellum. Pheladenia meaning false glands which is referring to the calli and deformis meaning departing from the correct shape or mis-shapen.
The labellum plays an important role in pollination; it is the landing platform for the insect. Depending on the process by which the flower is pollinated – or at least attracting the pollinator – this can attempt to mate with the labellum which it has confused for a female of its species (pseudocopulation), or can then feed on the nectar produce. Like many orchids Pheladenia does not produce nectar so the actual attractant for the insect is hard to determine.
The labellum is a distinctive feature of orchids. A modified petal, they are so amazingly varied and complex that botanists often provided detailed descriptions of the features which are present in various combinations, as a means of describing the species. Terms such as lobes, margins, gland/calli, hairs/vestiture/setae, longitudinal ridges, plates, auricles, spurs, papillae etc are used to describe the various features of the labellum.
Some of the features of the labellum of P. deformis are:
It is stiffly attached to the column, unlike Arachnorchis tentaculata which is hinged and freely moving
It is tri-lobed meaning that the labellum shape is divided into three distinct sections.
Unlike Diuris pardina where this feature is easily seen, it is obscured as the outer two lobes are erect and curved in so that it forms a trumpet like appearance with the column.
The margins or edges of the labellum have fine teeth which are slightly curved inward. The margins of Arachnorchis cardiochila are smooth-edged and curve outward from the ‘throat’ of the labellum
It has two types of calli, fleshy, non-secreting glands.
The ones at the base are not as easily seen but they are described as being papillae, e., small, irregular, pimple-like projections or bumps.
The more obvious ones that give the flower its bearded appearance are elongate and without a swollen head, like the bristles on a brush.
In contrast, Thelymitra does not have any type of calli, although it should be noted that calli do play an important role in orchid pollination.
The apex, tip of the labellum, is curved under (recurved to reflexed)
To see some of the variety of labella, Orchids of South Australia (Bates and Weber, 1990) have several drawings detailing the differences on pages 35 to 38, 81, 97, 104 to 106, 114, 119 to 124.
So why spend time looking at details of labella?
It is not important for identifying Pheladenia deformis but it can be a distinguishing feature for other species, for example, the lateral lobes of Diuris maculata are much narrower than D. pardina (Jones, in Harden (ed.) 1993); or the shape of the callus cluster on Chiloglottis which alludes to the species.
Reference:
Bates, R.J & Weber, J.Z. (1990) Orchids of South Australia, Government Printer, Adelaide
Brown, A., et al, (2013) Field Guide to the Orchids of Western Australia. Perth, WA: Simon Neville Publications
Jones DL (1993). Diuris in Harden GJ Flora of New South Wales, Volume 4. University of NSW Press, Sydney.
Jones, D L et al, (2006) Australian Orchid Genera, an information and orchid identification system, interactive CD-ROM
Thank you to Greg Steenbeeke for assistance with this article.
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).
Oligochaetochilus arenicola
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.
Urochilus sanguineus
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 movedAfter 12 minutes, labellum about to fallAfter 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!
NOSSA 