Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Tuesday, August 11, 2009

Ironbark Orchid from the Shoalhaven.

This is another of what I think of as "Alan's Orchids" - one which I only ever see if shown by Alan Stephenson. Alan is the Conservation Officer with the Australasian Native Orchid Society. He happens to live in the Shoalhaven region, and this plant and yesterday's related plant live in this region. He knows the area really well.

This plant is called the Ironbark Orchid (Tropilis aemula or Dendrobium aemulum) because it appears to have an obligate relationship*** with Ironbark Trees (Eucalyptus paniculata or Eucalyptus fibrosa). These trees are large Eucalypts with persistent, coarse fibrous bark.

Note the bud shape, thick stems and flat leaves.

In the Shoalhaven region, these Ironbark trees are relatively uncommon, and we only saw them in two locations some 40 Kms apart - interspersed with millions of other Eucalypts. When we found the second group of the Ironbarks, we got out and studied the trees for Ironbark Orchids, and there they were! Effectively this colony of Ironbark Orchids is an "island" within 160 Sq Kms of unsuitable host trees. How does that happen?
This plant has swollen base of the stems, as is clearly visible in this image.
It also has flattened leaves, which are roughly oval in shape, and are smooth and leathery. It is very different from yesterday's "Rat's tail Orchid" in both regards. That is part of the explanation of why this plant is now regarded by Jones and Clements as a different genus from the Dendrobiums. However, there is great similarity in flower shape.

Unfortunately, when I was there, none of the flowering plants were at low levels. In fact this Orchid is fond of growing quite high up, but there were some near ground level, just they were not in flower. This is as close as I could get. I need to go back again, now the lower plants should be open! One can discern the basic similarity to yesterday's flowers. The dorsal sepal is not as severely reflexed as yesterday's flower. The buds of both were quite similar (see top image, above).Here is a nice display of flowers growing on an Ironbark on a steep, rocky hillside. They were about 4 metres high.*** Obligate relationship: Symbiotic relationships - "obligate - i.e., necessary for the survival of at least one of the organisms involved".


Duncan said...

Enjoying your orchid posts Denis, you've certainly got some interesting stuff up your way.

Denis Wilson said...

Thanks Duncan
I've got to get back into local Orchids a bit more seriously.
These two were from Nowra (on the coast, an hour away).
My best local searching area has been ruled out of bounds by the Catchment people, unfortunately, so I have to find another area to go in.

Allen said...

Hi Denis, A fine posting of a delightful Orchid. The so called "Feather Orchids" are certainly worth looking out for. In the uplands near by we get a close cousin Tropilis callitrophillis but i have yet to see one myself. You have given me encouragement to seek it out. Appearently it favours Callitris macleayana upon which to grow.

Denis Wilson said...

Hi Allen
I will watch the Swampy Things Blog for a post on that one.
These plants do seem to be highly specific re their host trees. Knowing that would surely give you some chance of finding them.
Best of luck with your search.
I still wish to get some better photos of lower-growing plants.