Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Wednesday, October 01, 2008

Dendrobium striolatum

There are only a few Epiphytic Orchid species in the Robertson area. Two of them have just started to flower. Today I will show you Dendrobium striolatum (or Dockrillia striolata), the Streaked Rock Orchid. I will show you the other one in a couple of days.

This tiny Rock Orchid grows immediately below the exposed clifftops of the eastern-facing sandstone escarpment of the Illawarra Escarpment. They are lithophytes ("rock plants"), or "epiliths" (the term the PlantNET botanists use, but it is a less graceful term).

Growing on the coastal escarpment (only 25 Kms for the ocean), these plants obtain maximum moisture reception (from rain and mist). They are also protected from the hot drying sun and wind. Even so, they are highly adapted to moisture conservation. Botanically they are classed as "succulents", having what appears to be a plastic coating on their leaves. Their leaves are "terete" (roughly circular in cross-section, with some plants having a shallow furrow in their leaves). In many ways their leaves bear some similarity to the leaves of the garden plant "Pigface", which is an arid climate plant.

However, these plants are wet climate plants, being immediately above a wet rainforest, in a very high rainfall area. These plants receive moist sea breezes. But their roots have almost zero ability to access stored moisture (normally found in soil or leaf mulch). Here you can see them clinging to a vertical cliff face, more than one hundred metres above the valley floor below (in the Macquarie Pass area below). As with arid country plants, these plants must trap and conserve what moisture they can, and send roots into rock cracks, looking for any seepage. Click on the image, to see the flowering plants in the dark shade of the cliff face, with a hundred metre drop below them.These plants, growing in such extreme habitats, survive by having their roots penetrate cracks and crevices in the rocks. But, in this local area they do not grow on westerly exposed rocks which would be too hot and dry for them. In areas such as overlooking the Kangaroo Valley (which is a drier position than here) this species may be found on drier westerly facing clifflines, but only on the sheltered sides of rocks, or in narrow crevices between rocks, or in steep rainforest gullies. They are always close to cliff edges. These plants should be known as "fresh air plants" for they seem to always live right on the edge of a cliff.

Here is a freshly opened flower. The white labellum is just starting to curl back towards its fully reflexed position.This next flower is more reflexed, but the lateral petals are only just starting to flare out sideways.This flower is now fully mature, fully opened.
This flower has fully spread lateral sepals, and from the rear, you can see the diagnostic red stripes on the rear of the flower.Fortunately, not all these Orchids grow on vertical cliff-faces. Some were growing on rocks at the top of the cliff, and I could get close to them (with only a little difficulty). They are not a showy plant, but when you get close enough to them they are really quite charming, in their details.If you get "up close and personal" with these flowers, you can see that they are the "right way up" ("resupinate") which is the opposite of the large florist Orchids such as "slipper orchids" (in which the large, showy Labellum (the "slipper") is underneath the column (which is where the pollinia and the anther - the sexual organs of the flower - are held).

In order to see where the insects are required to enter these flower (to pollinate it) I have now pulled this flower backwards, onto its back (to the right), in order to show you the "working parts" of the flower. It is the same individual flower as photographed 2 images above.

I have labelled the main parts of this flower. The Dorsal Sepal which is normally underneath the flower, is now protruding to the left, exposing the column, and more importantly, the tiny opening where insects need to enter, in order to pollinate the flower. The Labellum (which was previously reflexed up and over the top of the flower) is now positioned to the right The entrance to the "column" (necessary for minute insect pollinators to enter) is in fact underneath the reflexed labellum. (Click on the image, to read the labelling).These flowers are tiny, and hard to access (on cliffs) but if you do get up close to them when they are flowering, you will be rewarded with a sweet perfume - the magic they create in order to attract the tiny insect pollinators.


Mosura said...

Great post and a wonderful orchid. You'll need to don some abseiling gear and get some more pics of the ones on the cliff ;-)

There are supposed to be some epiphytic orchids near here but I have not located them. I remember some beauties up around Tamworh and Manilla in N.S.W (if only digital cameras were around at the time)

Denis Wilson said...

Hi Mosura
Abseiling....If only.....
There are some (few) "Sydney Rock Lilies" (Rock Orchids) in the district, but I would need the abseil gear to get anywhere near them.
Thanks for the comment.
Ground Orchids are easier in this respect. At least one is not risking life and limb - just risking leech bites.
The books do say that this species (above) occurs in Tassie - a yellow, less streaked sub-species, apparently.

Duncan said...

Good to see you still calling it a Dendrobium, Denis. :-)

Gouldiae said...

G'day Denis,
Another beautifully detailed post of an interesting plant - great stuff. Like Mosura, as I was reading through, images of you dangling on a rope to get your photos were coming to mind. I don't mind how you do it, love your work.

Denis Wilson said...

People whoh fantasise about me hanging from ropes, over cliff edges do not know me well enough. I might have such fantasies, but only when peering over the top of a cliff, to catch a glimpse of "Sydney Rock Lilies" (such an annoying name, but it is an old Colonial name, so I use it).
Then the vertigo sets in, and i retreat from the edge, quivering like a scared puppy.

Duncan, I care less for the name Dockrillia, mostly through lack of familiarity with the tribe of Dendrobiums, which are mostly epiphitic and mostly more tropical. I do use the new names for the Greenhoods, because the tribe is so obviously diverse, and I feel they really do need to be broken up. But out of respect for users less familiar with the new names (and not everybody has the new books, or access to the Internet) I always show the old names and new names. And some of the new names are shockers anyway.
It is hard to love an Oligochaetochilus gibbosus, but the original Pterostylis gibbosa was never very user friendly - it is just we all grew up with those names. That allowed us to ignore the fact tht it made them sound like Dinosaurs, anyway.

You should not have got me started, Duncan!