The Den. teretifolium Complex

A BIT ABOUT . . . The Den. teretifolium Complex

© Gerry Walsh

Dendrobium teretifolium var. aureum. Or: Dendrobium dolicaphylla

Var. Aureum specimen plant, Kroombit Tops 2012

  1. teretifolium var. teretifolium Rainforest Form.17 Blooms on Raceme

Dendrobium teretifolium var. teretifolium in the wild.

WHILE I’ve been attempting to discuss something of interest about selected native orchids, via my handle “A Bit About” I have side-stepped the Dendrobium genus quite deliberately. More than enough has been written about that section of the native orchid world, and unless I can think of something new that hasn’t been tossed about in print before, I don’t bother boring people with rehashed info.

Having covered various other genera, I capitulated and decided to consider good old Dendrobium again. Just in  case something of interest did lurk within. When I started thinking about D. teretifolium it dawned on me just how complex  this species really is. And the more trips I make into the wild country of this great land, the more confused I become. So perhaps it’s time to return  the “rat’s tail/pencil/bridal veil” orchid to the courts for re-assessment.

Over the years, but particularly of late, there have been more changes to the status of D. teretifolium than there has been post-war Italian governments. Well, not quite, but perhaps more than with nearly any other species of native orchid having a ” complex” tag tattooed on it. In one form, or variety, or sub-species, or species, or even flavour I suppose, you can see D. teretifolium from  about Narooma in southern NSW, then up north to virtually the tip of Cape York Peninsula. And nowhere is there a break  without some form or other of this species over that vast range.

The one thing that all of this complex complex (repetition intended) has in common is the leaves. These are always  cylindrical with no groove or seam anywhere around the surface. Other than this, it is pretty near impossible to claim  another feature that is constant across the whole range. D. teretifolium leaves are not always long, they are not always  green, they are not always thin, and they are not always pendulous (but nearly so).

It is tiresome to do so but I should go through, ever so briefly, the major forms of this species. Firstly we have var.  teretifolium. Broadly speaking, this form is supposed to occur on Casuarina species, mainly C. glauca, from Narooma to  around Morton Bay, or Brisbane if you prefer. Some authors report it as occurring as far north as Fraser Island. It is supposedly found only at or near sea level and is usually associated with estuarine environments.

This form is the real showoff of the complex and can have literally thousands of blooms on a large specimen. The other  forms can only produce about 20 per cent, maximum, of the number of flowers that an equivalent size var. teretifolium can  churn out. It is generally the first variety to flower in the bush house, starting in about late August here in Sydney.

The other commonly observed variety in NSW is the var. fairfaxii which is normally referred to as the rainforest  form. This form has been given species status of late as Den. fairfaxii. It is certainly not restricted to rainforests however and can be found from near sea level up to 1000 metres or so into  the clouds. Neither is it restricted to trees – it frequently colonises rocks and occasional large colonies can be found on rock  outcrops in open forest.

Var.faiifaxii is found from the Blue Mts (where it can be locally common) up to around the Clarence River  just north of Dorrigo. It is easily distinguished by it’s habit of only having two or three blooms to the raceme. These can be up to 9 cms across but frequently less. Whilst they are quite attractive with their snowy white blooms with red striations,  the plants don’t have the ability to cover themselves in the manner of var. teretifolium. There have been very rare exceptions to this statement however.

A clump of var. fairfaxii can grow to an enormous size and it is one of the joys of nature to stand under an old-man Fig Tree and feel dwarfed by the great chandeliers of bridal veil studding the gravity-defying limbs. Some such clumps would be quite able to fill up a Holden ute.

The longest (most pendulous) plant I know of grows only a stone’s throw from the shores of Lake Burragorang in  Water Board catchment, where I accidentally strayed four or five times in the late eighties and early nineties. By placing a  stick, the same length as myself, in amongst the huge specimen, Dennis Johnson and myself (who had accidentally strayed with  me on one occasion) were able to deduce that this bridal veil was around 4.5 metres from top to bottom. It is still hanging  up on that rock and every year I think about straying back for a look during the flowering season. But it’s a long, hard  journey to that mountain creek and I haven’t been lucky enough to get lost in the catchment areas for a good while now. And besides, it is an offence to approach stored up Water Board Dams inside a distance of three kms. So don’t get lost like i have, a few times . . .

The other well known variety of D. teretifolium is the var. aureum. These days we call this form D. dolicaphyllum, a species in its own right. This form is rather similar to var. fairfaxii with  the exception of its colour. As the name suggests, its flowers are ‘aureum’ or gold in colour. As well, the red striations in  var. aureum seem to be wider and more intense. This combination is extremely appealing and a heavily flowered specimen  (not a common sight unfortunately) is a joy to behold.

Var. aureum extends from the Richmond Ranges in northern NSW to at least as far as the Eungella district near  Mackay. But it becomes difficult to recognise a singular form of var. aureum because every few hundred kms it seems to  mutate with differing floral characteristics. The flower form around the State border is certainly much larger than the form from  around Kroombit, or Gladstone, which in turn is different to the form at Eungella, or Mackay, where in fact there may be several forms. Between  these distinct regions there are suitable areas where no var. aureum exists at all. So it all becomes quite confusing.

In north Queensland we find the variety fasciculatum. This is yet another one which now has its own species status as Dendrobium calamiforme. This is the thick leafed form that grows on many street trees  in Cairns, on the Esplanade for example. These leaves can grow to 10mm thick and large plants of var. fasciculatum have a  great deal of bulk compared to all the other forms of D. teretifolium. It is readily distinguishable when in flower because it has long racemes of closely packed, small (about 12mm) white flowers (up to about 15), that do not open up very widely.  Unfortunately, it is a difficult form to flower down here in Sydney. Despite having several very robust clones for many  years I have never been able to flower them.They need at least an unheated glass house in this part of the world to trigger  flowering.

I have often heard it said and read that the thick leafed plants are found only down on the lowlands and, as they ascend  into the mountains, var. fasciculatum becomes thinner and thinner until it resembles a typical southern var. fairfaxii in  vegetative form. I was sitting on a rock on a mountain up on the Atherton Tableland a few years back (contemplating  the meaning of life no doubt). I was  very surprised to discover a  typical lowland plant with 9mm thick leaves, growing on the same short  tree limb as three thin plants with only 4mm wide leaves. It was the only thick leafed plant I observed during that whole day.  There were hundreds of the thin leafed types around the surrounding bush. None were flowering unfortunately so a comparison was not possible. I found this incident rather perplexing.

Note: Bailey described a form of D. teretifolium from the tropics as D. baseyanum back in the 1800s. No one has been certain exactly what constituted D. baseyanum and its name fell out of use. These days there is a line of thinking that suggests that the upland thin form of D. teretifolium, from the Atherton Tableland region, is no doubt what Bailey was describing. I am not a botanist: I have nothing to add to this information. However, the thin form IStotally different from the lowland thick form that it would seem likely that Bailey was referring to this thin leafed form.

There is another form of D. teretifolium that is quite common in some areas, but which I can never decide what pigeon hole to stick this one into to. I refer to it as the rainforest form of variety teretifolium. However, it is certainly a far cry from most growers understanding of that variety.

This enigmatic rainforest form looks exactly like var. fairfaxii vegetatively speaking. It grows in rainforest situations and occasionally on rocks in or near rainforest. It can be observed at up to 1000 metre altitude, just like var. fairfaxii. When in flower however there is no resemblance whatsoever. This rainforest form produces racemes up to 15 cms long supporting up to 15 flowers, all spaced well apart. This is totally opposing the two flowers that is generally found on var. fairfaxii. Also, it is very different to var . teretifoliums five to ten blooms on a much shorter raceme. Flowers are similar however but much more crowded together.

This rainforest form can be found from around the Macleay River, Kempsey NSW, up to Kroombit Tops near Gladstone in central Queensland. It is hap hazard in occurrence however. It is certainly common in such areas as the Clarence Valley, the Jimna Range and the Calliope Range near Kroombit. No doubt it is abundant in many other regions within this distribution.

The rainforest form grows on rocks quite commonly, as well as trees, and is a far cry from the appearance of the coastal form of var. teretifolium. I simply cannot believe that it has not been recognised by the botanical hierarchy of Australian science. I think it is a case of them simply having no knowledge of it at all.

There are other strange forms around the countryside including an interesting form that was thought to be restricted to the Penrith district near Sydney. It does extend down to the south coast of NSW however. It grows horizontal, outwards, and seems to be fighting against becoming pendulous like normal var. teretifolium.

It seems pretty well restricted to Casuarina species. It does grow right into the harsh dry country to the south of Sydney and Camden, at considerable distance from the coast. But does occur around the Jervis Bay and St Georges region in typical salt and brackish water courses as well. It covers itself thickly with enormous numbers of snowy white flowers. An old man specimen may only be a metre deep but also it can support itself while growing a metre horizontally out from the tree trunk. It looks fabulous! Unfortunately it is poorly understood by most growers.

I do not grow hybrids at all but I find it fascinating how easily all forms of D. teretifolium seem to readily hybridise with other members of its section ie: Section Rhizobium. Natural hybrids in which D. terefolium has been matched with other species include: D. striolatum, D. schoeninum, D. mortii and D. pugioniforme. It has also been matched with D. linguiforme var. nugentii from around the Atherton Tableland. This natural hybrid was always uncommon but enough exist that it was given the name of D. X grimesii. (Capital X meaning that it is a naturally occurring hybrid). (A small x indicates the cross is a manmade hybrid).

Interestingly, I have a plant from the Sussex Inlet region, 200 kms south of Sydney, that is a natural hybrid of D. teretifolium var. teretifolium X D. linguiforme var. linguiforme. It is the only one that has ever been found so far as I know. Is this specimen to be known as D. X grimesii? The two parents are not the same taxa as the two parents of the D. grimesii plants from the Atherton Tableland. 3500 kms separates these plants. I am not sure what to call it . . . but I am really glad I have it!!

In cultivation you would think that all the variation in the D. teritifolium complex would present some issues. That is not the case however. It seems to not matter where it comes from in this great nation; they all respond to the same cultivation techniques. The main thing to remember is that this is a species that will grow quickly and with very little in the way of problems. It is as tough as old boot leather and when it gets going it will grow large in quick time.

Choice of a host is not a problem when mounting D. teretifolium. I like to use natural lumps of Portuguese virgin cork if possible. This material is expensive so for a cheaper alternative you could try nearly anything you find laying around. I think you could use an empty beer bottle and you would still have success with D. teretifolium. Long lengths of old hardwood are good. So too are long pieces of hard treefern fibre.

You can tie the plant to a new host without the addition of moisture retentive moss or similar.  But a little sphagnum draped loosely over the root system may be a bit of an encourager for quicker root production naturally. But if you do not then do not panic about it. Things will still go well. Use a long lasting host however because this species does not like to be disturbed once it settles in for a while.

Another interesting way that works very well is this. Grab a 200 mm squat pot and cut a hole in the base just wide enough to feed all the roots of your D. teretifolium plant into the centre of the pot, through the hole you created. Attach three wires to the edge so you can hang it up high. Fill the pot with chunky orchid bark and thats all you need to do. This is a good way to handle large specimen plants that may not have too many roots. Such plants can drop half their long cylindrical leaves in quick time if they lose too many roots. The new roots run wild through the bark and over the outside of the pot like crazy.

While D. teretifolium is generally as tough as nails it pays well to be quite cautious when handling a large specimen plant. A two-metre-long bridal veil specimen may have several kilos of weight hanging off just three or four thin wiry stems originating from the root mass. Too much twisting and they can snap off very easily. The loss of one of these main stems can remove a lot of the mass of your big plant with one wrong move. You have been warned people.

So if you wander around the bush looking for fallen limbs etc. in the hope of finding salvage plants that need to be nursed, then be exceedingly careful with your technique. Take your time and take note of exactly where each leaf is attached. Many a plant if destroyed when a grower with buck fever starts to grunt and groan and pulls the wrong limb or stem in their haste. The more roots you save the better for the plants well being . . . and yours!

And finding plants on fallen trees and limbs you surely will do. D. teretifolium is a species that can proliferate itself dramatically. I have seen some rainforest and bushy areas where there must be thousands of seedlings to the acre and growing on bark and rock alike. After many trips to the Kroombit Tops region I have seen fire ravaged seedlings of D. teretifolium sprout out and come to life in double quick time. A really hot fire will kill them off of course. But a normal kind of slow moving fire only singes them in the main.

Seed pods of wild plants are extremely abundant. Quite literally there will commonly be dozens of seed pods on even small plants of D. teretifolium. I suspect that there are many different insects attracted to the honey like perfume of this species. Pollination is astonishingly frequent. The resulting establishment of thousands of seedlings can easily be understood. D. teretifolium is an extremely resilient survivor.

Like all other orchids in this world, a fast growing, large bulky orchid like D. teretifolium requires plenty of tucker or they will not grow to full advantage. So feed them up often. But even if you forget to feed they will still seem to go OK and flower each year. Flowering performance and floriferousness will be greatly enhanced if you grow your plant is strong light. They can take it. Once they are established then they could even do well in all but the hottest summer full sun. What a species is the Bridal Veil Orchid!