As the name would suggest, this variety is restricted to a small area of the Central Highlands of Queensland known as Carnarvon Gorge. The gorge sits 300 kms or so inland of the coast, and just south of the Tropic of Capricorn. The nearest large town is Emerald to the north and the small town of Injune is to the south. Although it is a considerable distance inland, it is still on the coastal watershed of the Great Dividing Range. At Carnarvon Gorge, the Great Divide is at its farthest point from the coast along its entire traverse of Australia.
Carnarvon Creek drains a large area of connected gorges and canyons that cut deep into mainly white sandstone plateau. It is literally an oasis surrounded by much drier countryside. The Gorge contains many plants and animals that occur nowhere else or are disjunct from larger populations either to the north, south or east.
There are really no distinguishing characteristics that make var. carnarvonense stand out from other varieties. Pseudobulbs reach a maximum length of around 30 cms to the first leaf. Leaves are indistinguishable from other varieties. New growths tend to have a purple pigment in the manner of var. blackdownense, but not nearly so strong. This pigmentation disappears when growths mature. Bulbs are roundish in cross-section, not ovoid.
I have noticed a tendency for var. carnarvonense to have eyes along the nodes of the pseudobulb to a much higher level than normal. Occasional new growths will appear from eyes at equal distance between the roots and the leaves. Plants noticed on my visit to the gorge suggest a habit similar to the D. kingianum var. carnarvonense from the Gorge. That is; many tend to have untidy habits, with new growths appearing more like aerials from any node/eye along the pseudobulb. This leads to a clinging habit, rather than a clumping habit if that makes sense. In the bush house this habit tends to disappear with the years.
I hate to have to say it, but, judging by the forms that I have seen over the decades, you would not be growing var. carnarvonense if you were chasing award winning D. speciosum. That is not to say that some shapely plants do not exist. I just think the chances would be low. You only really grow this variety because it is a rarer denizen in collections.
Flower colour I have seen is fairly similar right across the board. That colour is basically off-white, not really cream, certainly not pure white, and never yellow. Shape is generally spindly, often unsymmetrical and unimpressive.
Size is OK, they are not small, and flowers to 50mm are not uncommon. Raceme habit is acceptable enough and nice arching spikes with plenty of blooms can be expected. The peduncle is short and racemes will occasionally be up around 400mms. Alas, there is not much else that needs to be said.
Carnarvon Gorge is quite an extensive system of beautiful, deep, narrow canyons and cliffs but in global terms, it is a tiny area to support a distinct variety of D. speciosum. The Gorge is around 30kms in length from its source to where it eventually breaks out onto the surrounding plains. Many plant and animal species exist nowhere else but in this gorge. Some examples of the isolation and evolutionary separation include many fern species, palms, cycads and quite a few tree and shrub species.
Epiphytic orchids are included and the Gorge contains Dendrobium kingianum var. carnarvonense, Sarcochilus ceciliae, S. dilatatus, Plectorrhiza tridentata, Cymbidium canaliculatum and of course D. speciosum var. carnarvonense. During my only visit to the gorge, in November 1995, we were privileged to see all these in situ. I know of no others epiphytic orchids in the Gorge but there may be a Dockrillia, either linguiforme or bowmannii being the likely candidates.
On that visit we did see two specimens of var. carnarvonense growing on the trunks of trees, around two metres off the ground. This was in perhaps the moistest portion of the Gorge. I would think it unlikely that there would be any more epiphytic var. carnarvonense examples in the whole gorge.
In August 2012 we ventured into the drier western portion of the Carnarvons, known as the Mt Moffatt Section. Really it is only just over the ridge dividing the eastern and western watersheds of Qld. By road it is about 450kms. We wanted to see if the habitat could support var. carnarvonense. As the crow flies it is only a few kms. But what a difference a crow can make. Dry, inhospitable countryside was all we found but there may well be pockets that could hold D. speciosum. After the massive floods of last year, many roads leading into the high country had been closed for months. What we could see was totally discouraging however.
To sum it all up, you have to be a complete speciosum nutcase to pursue var. carnarvonense. I will put up my hand first: all nutcases line up behind me please. It is quite uncommon in cultivation and will always be very difficult to obtain specimens if you decide you are indeed a nutcase yourself.