3 variations that contribute to D. speciosum var. boreale
Speciosum var.boreale is distributed from the mountains just west of Townsville, Queensland, northwards to roughly the Big Tableland which is just south west or Cooktown. Mt Elliot and The Pinnacles region in the south are the southern limit but it may well be that var. boreale extends south of these known regions. From the Bruce Highway, a series of high peaks extend southwards from Townsville and there may very well be isolated pockets about these peaks. Many have no visible access and local knowledge would be needed to investigate. Var. boreale can be found from nearly sea level to over a thousand metres altitude and westwards to the Mt Windsor Tableland.
Variety boreale is certainly a contentious one. It is a variety with extremely variable physical characteristics. Some are short and stumpy while others are thin and weedy. Others are as fattened up as the best forms of var. speciosum from NSW. Some are so long and lanky they could be confused with var. hillii. This variation of forms from the northern tropical area can often cause consternation when deciding just what variety of D. speciosum you may be scratching your skull over.
Some years ago, much work was undertaken by two gentlemen with vast experience in the botanical field. Each has had his work published and if you happen to pick up the work of one of them and then the other, you may well be pondering the situation. I am here to try and clear it up to some degree if you are one of the head shakers.
The David Jones way: 3 species
David Jones assigned new status to three forms of this enigmatic variety of D. speciosum. He gave them new genus and species status. I will attempt to very briefly outline what his opinion is. I should say right now that these mixed up types were formerly included with var. curvicaule in the text books. Very few people with knowledge were happy with this and I was one of them. Variety curvicaule is not found in the wet tropics and is isolated to the vicinity of Mackay, some 350 kms to the south of var. boreale. See distribution map.
Thelychiton curvicaulis (not curvicaule) is by far the more extant form that Jones deals with. It has short to medium length pseudobulbs. Growth habit is either thin and weak, or average in robustness without being grossly thick. The pseudobulbs are close to round in cross section. It is found from the Townsville district right up to the Atherton tableland and just above sea level in some parts to over 1000m altitude.
It is mostly found on rock but if suitable emergent trees occur in the forests it will take to the air as well. Much of the rainforest up that way is extremely even in the height of the canopy and so emergent trees are not common. Emergents are needed for the var.boreale/curvicaulis to form arboreal colonies and you go for miles in the rainforest without seeing any D. speciosum at all, unless you locate rock face within the rainforest or an oversized tree somewhere that has climbed into the sunshine.
Thelychiton rupicola is quite common within a limited range and is very robust and has quite swollen bases on its pseudobulbs. It seems to be restricted to growing on rock substrates. It only rarely occurs on trees and in discussions with several experienced observers I could only confirm a single specimen, photographed on a tree. It is limited in its distribution, according to my observations at least, and it would appear to be most common on the eastern side of the Lamb Range at moderate altitude. This is puzzling because very suitable rainforest trees exist all around the rock faces where I have seen large and healthy clumps of this type of D. speciosum for miles.
Thelychiton biconvexus is entirely different in appearance to the other two Jones types. Its bulbs are greatly elongated and are thinnest at the base and thickest just below the leaves. The bulbs are very ovoid and sport almost sharp edges. The leaves are often quite large and supple. The bulbs are frequently over 600mms long to the first leaf and even longer. Where I have seen it, it is equally common on both trees and rocks. It is most common north of a line from Mareeba to Mosman but is also present in the hinterland behind Tully and Babinda.
The Peter Adams way: One variable variety of D. speciosum (var. boreale)
Peter Adams on the other hand has done a lot of exhaustive research on this tropical form of D. speciosum using very exacting scientific methods, including mathematical analysis. His conclusion is that all these different growth habits are actually representative of a single, but extremely variable variety of D. speciosum. He classes them all as Dendrobium speciosum variety boreale. Boreale literally translates as NORTH, or northern, quite a good way to sum it all up. Adams also maintains the Genus Dendrobium.
For what it may be worth: The Rock Lily Man has a view . . .
I have thought this problem over for years and my conclusion is that I prefer to support the notion of a variety of D. speciosum rather then separate species. To me they are all quite obviously representatives of D. speciosum at varietal level only. However, in my mind, and in the mind of many others, I accept that it is fairly easy to see that a particular plant of var. boreale is a northern one, a Lamb Range form, or the more southern and widely spread form.
I freely admit that I do not have the intelligence or the training to investigate the situation beyond an opinion purely based on in situ and bush house observations. Please make a careful study of the photos on this web site and form your own opinions. And let me know what you come up with.
I cannot help but think that the ground breaking grandfather of much Australian Orchid investigation, Alick Dockrill, may have ended up happy with something along the lines of: Dendrobium speciosum var. boreale forma biconvexus, forma rupicola, and forma curvicaulis. He in fact applied this idea to some other species: most notably the Dendrobium teretifolium complex. Example is D. teretifolium var. fairfaxii forma fairfaxii; and forma aurea. Today these plants are generally accepted as species in their own right. The genus Dockrillia, which accommodates the terete leaved species, was strangely enough, rejected by Dockrill himself but, none the less, remains in common usage to this day. Come back Alick!!!!
In all that you have read above, to try and understand var. boreale, I have not written a word on the flowers, only the vegetative features. I have deliberately steered away from the floral aspects of the three forms up to this point. Now I will have a go at stunning you all with this side of the argument. This is rather simple to do actually. The reality is that I cannot see much difference between the floral attributes of the forms that make up var. boreale. They are so similar its ridiculous to even say there are differences, beyond the normal variations found from plant to plant in populations of any variety of D. speciosum.
Flowers are white in the main but light cream/yellow will occasionally be seen. They are not particularly large, but they may reach 30mms across and up and down. Often they are smaller. Adams points out a very relevant feature that you should remember when identifying var. boreale. If you draw an imaginary curved line around the tips of the flower segments, you nearly always end up with a circle, not an oval shape. This is perhaps the easiest way to do a quick ID on the specimen in front of you. It is not infallible but rarely is this simple investigation wrong.
Also, var. boreale has roughly one third of its raceme devoted to the peduncle. The peduncle is the space between the leaf axil and the first flower up the raceme stem. All other varieties of D. speciosum have short peduncles by comparison, excepting of course var. pedunculatum. Racemes can be moderately crowded or sparsely flowered.
Some forms have extraordinarily upright habits. One given to me years ago by Ted Gregory he called KIRRAMA has the most upright habit of any speciosum I have ever seen. If it starts out at an angle, it will soon turn perfectly up to the sky . . . amazing! The markings on the labellum of var. boreale are nearly always strong and obvious, rarely pale. The roundness of the blooms and the lovely imagery of the white flowers make var. boreale quite desirable.
What can I say? Vegetative characteristics are simply all over the shop! Tall and swollen, short and thin, and fat as hell and massive, you have it all there with var. boreale. Some have huge flaccid leaves that you can roll into a cylinder and still others have brittle leaves that can barely be bent at all. Check out the photos above and in the main menu under the In The Wild Pics section.
Var. boreale does do one thing that other varieties of D. speciosum rarely do. Plants will often throw aerials, big aerials. When I was looking over a large colony in the southern Atherton Tableland a few years back, it was obvious that many of the specimens I was viewing were aerials that had fallen down from bigger plants just above, then taken root to the fern encrusted rock face.
Var. boreale will frequently throw aerials in the bush house as well. It actually becomes a menace and I am forever sticking aerials into pots of orchid bark. They usually establish well and then take up my precious bench space. But what a great survival mechanism to have? The thick bulb type of var. boreale, or as Jones calls it, rupicola, does not have this ability however. This is just another confusing piece in the jigsaw which makes up the rich tapestry of var. boreale . . . how poetic is that?!