Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Saturday, July 07, 2007

The Nature of Orchids of Robertson.

I wish to acknowledge the inspiration and assistance of two Australian Orchid enthusiasts and inhabitants of the Internet. One is "Gaye from the Hunter", whose blog "Hunter Valley Backyard Nature" has featured a section on the biology of Orchids, which is well researched, with excellent "links" to other scientific papers.
The other is the owner of the excellent Website "banjorah.com"
That lady has excellent Orchid photos, plus a very useful section on her webpage, called "Orchid Facts" which has various illustrated photos of Orchids with their parts named. (That section works best if used with "Internet Explorer"). In several of my illustrations I have followed the lead set on her website.
Classic Orchid "parts"
illustrated (D. Jones ***)

Last Thursday I gave an illustrated talk to the Austalian Plants Society, Southern Highlands Branch, about Orchids of the Robertson area (Robertson and Kangaloon).

About 55 people braved the cold of Moss Vale to attend the talk, for which I was very grateful.




Stylised structure of
the symmetry of an
Orchid's flower.
I began the talk with some brief discussion (and illustrations) of the "parts" of an Orchid flower, as I know this is a bit of a block to most people. The strange names used by "Orchid people" confuse some plant enthusiasts.
I like to start my discussion from "first principles" of plant biology, where possible. In simplest terms, the sexual organs of the Orchid are combined within the central part of the flower. This is known as the "column". It includes the pollen-bearing organ (the male part) and the stigma (the female part) which most people never get to see, but which, of necessity, is of vital interest to insect pollinators. Usually the attraction comes from scent glands, although some Orchids (such as Potato Orchids) have evolved other attractions, (in that case "pseudo -pollen")
It is never that simple!
Here is a diagram of how the common "Ladies Fingers" Orchids have evolved differently from the classic structure. The red arrows indicate the variation of position from the "standard model" above.

I showed a collection of photos of 37 species of local Orchids. There were only two species of which I have photos, which I did not show.

I am hoping to add greatly to my "collection" of species over the coming winter and spring seasons.
Partly this is due to the fact that I now own David Jones's (***) wonderful Orchid book "Complete Guide to Native Orchids of Australia". This book is wonderfully detailed and is the best reference text which is currently available, for native Orchids of Australia.

Armed with this book, and a magnifying glass, I hope to make more sense of the Orchids which I will find. It has all the "new names" which the taxonomists have come up with, as they have reclassified the various types of Orchids. While I am not enamoured of "splitters" generally, some of the old Orchid genera, such as "Caladenia" which included the common "ladies fingers" types and also the elaborate "Spider Orchids" were desperately in need of revision. Similarly the Greenhoods and Sun Orchid groups.
Now for a real flower.
It is "Never That Simple"
Glossodia minor
(Click on photo to enlarge)
The "sepals" form the outer protective coating of the flower, when it is in "bud" stage. As the flower matures, and opens, they develop their characteristic shapes and colours, different for each species of Orchid.

This Glossodia flower differs from the sketched "Caladenia" type of flower (sketched above and photographed below) in that it does not have the Labellum as a dominant structure. It is there, just less dominant. It is in the classic position, underneath the "column".
The Labellum is a modified petal. Thus Orchids can be seen to have 3 sepals and 3 petals - one of which is usually, but not always, heavily modified. (Sun Orchids have almost exactly similar petals and sepals - without a characteristically shaped "labellum"). Thus they are more "regular" than most other Orchids.
The Glossodia flower is interesting in that it has two really obvious "calli" or glands (easily seen if you clicked on the photo).
Pale pink Petalochilus species.
If you click on this photo you will see that "Caladenia types" have rows of "calli" on their Labellum which act as something which David Attenborough (in his "Private Lives of Plants" TV documentary series) described as like "landing pads for insects".

This is a pale pink form of Petalochilus carnea (as far as I can work out).



It is "Never That Simple" (again).
Greenhood Orchid
seen from above.
They have
"special names" for
their parts too!
Greenhoods such as this Superb (or Cobra) Greenhood (Diplodium grandiflorum) have fused the two free Petals and the Dorsal Sepal into a "hood" structure. The "Labellum" (so dominant in "Slipper Orchids" for example) has become an internal structure, which is movement sensitive and motile. It senses an insect's presence, and snaps back into a closed position, to trap an insect pollinator, preventing its departure until it has been dobbed with the "Pollinia" - a sticky package of pollen which all Orchids produce.

Here is a side-on photo of the same species, which shows the erect "labellum" inside the flower. The shape of the Labellum, and whether or not it protrudes, is one of the diagnostic features of the Greenhood group of Orchids (many of which are not "green" by the way).

The front section of the flower is formed by the Lateral sepals, of which the lower sections are fused to form a structure called a "sinus", while the upper parts generally protrude to form the "points" (sometimes called "ears").


"Silhouette" of the Labellum
of the same Greenhood


Forgive me for one "art shot" - an almost accidental silhouette shot.
It happens to show well the raised Labellum of this Greenhood. I like the interesting visual effect, anyway.






Tall Greenhood with Labellum open
and then another shot when the labellum
has snapped closed.

The unfortunately named Bunochilus longifolium.
Perhaps I should not criticise this name, for the earlier name, Pterostylis longifolia never exactly tripped off the tongue.


This tall "Greenhood" does have quite long leaves along its stem, which make the plant quite readily identifiable, even when it is not in flower.

It is "Never That Simple"
- even less so, now!
This Small Tongue Orchid (Cryptostylis leptochila) is one of a group of Orchids which have reversed the "typical" structure, with the Labellum on top. In fact, according to the experts these Orchids are the "right way up". Apparently most "normal" Orchids actually twist as the flower matures, to put the Labellum underneath the Column. There are many genera of Orchids in Australia which are oriented in this way - "Leek Orchids", and "Duck Orchids" are two other groups amongst the local Orchids which are oriented that way.

Confused? Don't worry - we all are, a bit, at least. It takes time, but it is worth persevering with.
Chiloglottis reflexa
The complexity of Orchids always teases my sense of "wonder" - because of how complicated they have managed to become. I have only begun to scratch the surface of that discussion, here. For their evolutionary adaptation has taken them to great heights amongst plants - where some even have developed glandular modifications which physically resemble insects, as well as emitting appropriate odours to further complete the mimicry. This plant is in the group of Ant or Wasp Orchids. The structure resembles an ant or a female wingless wasp, but it is a structure of glands called "calli" on the Labellum of the Orchid. Calli is plural of "callus", meaning a swelling, or growth.

These Orchids then rely upon confusing male insects to such an extent that they attempt to mate with the flower, in the belief that it looks like, and apparently smells like, the appropriate female insect (mostly wasps). This process is called "pseudo-copulation", and is surely the ultimate in plant mimicry. How and why do they do it? Our imaginations can only guess at the answer.

I am not attracted to Richard Dawkins "Blind Watchmaker" model, but the main thing is our inability to imagine the possibilities which can arise over a length of time such as 65 million years, which is apparently the length of time since Australia apparently split from Gondwana. If we cannot "imagine" that time span, how can we imagine the possibilities of evolution which might have occurred within that time span?

Instead of finding it necessary to "understand" all of these issues, I prefer to enjoy the sense of "wonder" which is triggered by contemplating such tiny puzzles as these bizarre Orchid adaptations.

1 comment:

Gaye from the Hunter said...

hi Denis,

I enjoyed your orchid entry very much, and will no doubt re-read it several times and refer to it for future clarification when I am in doubt.

Thank you also for your mention and link to my nature blog. I believe that we nature enthusiasts can make a positive difference regarding awareness and appreciation of the nature we live amongst, and therefore, make a contribution to the future wellfare of our planet.

Regards
Gaye