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The gold standard for a species is the type specimen. This is the first specimen of the species collected, analysed and scientifically described and as such becomes the reference specimen or collection by which the identity of a taxon is determined.
No less than Sir Joseph Banks himself collected the type specimen of Dendrobium canaliculatum, from the Endeavour River, Cooktown in 1770 whilst the ship The HMS Endeavour was held up to repair damage from running into a nearby coral reef.
Tea Tree Orchids from this area today are generally* (*please note discussion of intergrading of varieties under Dendrobium canaliculatum var. tattonianum HERE) similar to the variety that extends northwards up Cape York Peninsula from about the Bloomfield River and Palmer River and into the Torres Strait. By convention, if a species (canaliculatum) is to be split into varieties, the variety that includes the type specimen must be the type variety (var. canaliculatum). The southern limit of seemingly pure var. canaliculatum appears to be about the Desailly Range just north of Mt Carbine - albiet recognising no clear-cut boundary exists.
Plants of Dendrobium canaliculatum var. canaliculatum have dark brown/ blackish purple striations on the sheathing of the leaves over the pseudobulbs and often dark edges to the leaves. Leaves may take on an olive to blue-grey colouration. They are abundant in many of the Melaleuca viridiflora forests on Cape York and also on other Melaleucas, fibrous-barked Eucalypts and also sometimes on shadier trees on the ridges such as Burdekin Plum. The climate of the Cape is very extreme with dry season fires and dew-falls seeming to limit the occurrence of this orchid in some areas where all other indications suggest they should flourish.
The flowers of var. canaliculatum are highly variable with the colour of no two flowers being completely the same. The range is typically brown to ochre red to gold to yellow (including some canary yellows) and yellow-greens, with the basal portion coloured and only rarely approaching pure white (var. tattonianum always has a pure white centre). For those var. canaliculatum plants which appear to have pure white centres, closer examination (generally will require magnification or a macro photo image) will show the colour fading to the centre and an off-white basal colouration.
A variety of colour forms in Dendrobium canaliculatum var. canaliculatum. Apologies for the poor photography skills - I will try to gradually substitute in better ones. Unlike variety tattonianum there is almost continual variation in the colouration of the flowers - seemingly no two flowers are identical. CLICK ON THE IMAGES TO EXPAND AND VIEW.
Whatever the colour scheme I consider a distinguishing feature of var. canaliculatum is that the colour on the tips of the flower 'fades' into the centre as opposed to var. tattonianum where the colour cuts off abruptly before a pure white centre. In some of the intergraded plants from around Cairns and north that appear as mostly var. tattonianum the colour on the flower tips 'tapers' into the whitish basal colour - something that is never seen on the pure var. tattonianum from the south of the range. Occasional plants as far north as the Lakefield area appear identical to var. tattonianum. Only very close scrutiny will show the 'taper' or 'fade' of the yellow to the whitish (never pure white) centre - unlike true var. tattonianum. It can be very subtle (like on the Laura plant in the image below) however on most plants a fade or taper will be quite obvious if one is looking for it.
I accept that use of the two images below is not a fair comparison (it should be the two flowers side by side in the same photo to ensure lighting etc. are identical). However this is all I have at this stage. LEFT: Plant is from Laura (most plants in the area are typical var. canaliculatum colourations), and looks to the naked eye (at least to mine) as typical var. tattonianum in colouration. RIGHT: Plant is from near Townsville (true var. tattonianum). The difference is in the transition of the colour on the tip of the petal to the white (var. tattonianum) or whitish (var. canaliculatum) centre.
Enlarged sections from the images above. In the interests of disclosure I have played with the contrast slightly in the enlarged sections to try and best show the difference.
On the flip side to the above, some intergraded Dendrobium canaliculatum var. tattonianum plants from the northern part of this variety's range (e.g. Mareeba, Port Douglas) have strong brown colouration on the tips of the petals and sepals (similar to var. canaliculatum) yet retain the pure white centres and relatively abrupt colour cut off of var. tattonianum. The visual contrast of the darker coloured tips to the pure white centre can be quite startling and attractive, and is distinct from true var. canaliculatum plants from further north.
The labellums of Dendrobium canaliculatum var. canaliculatum display yellow, brown and sometimes red colouration over a whitish or cream base. The typical purple disk on the labellum of var. tattonianum is usually present, however often reduced in size, sometimes to just a couple of purple spots. Petals and sepals of the flowers are broader and generally shorter than the better known var. tattonianum. Flowers are often closely bunched on relatively short racemes, however longer racemes with well-spaced flowers are not uncommon. I have seen just over 40 flowers to a raceme, which is exceptional for this variety. Average flower counts seem to be lower than for var. tattonianum, likely in the 12-20 flowers per raceme for a mature plant. Flower substance is generally superior to the other variety.
I have never read or heard any reference to differences in the scents of the flowers within Dendrobium canaliculatum. However it has become apparent to me that the scent of var. canaliculatum flowers is also different to var. tattonianum. It would be described as less sweet, with a more musky scent something like a more pleasant Dendrobium johannis, or perhaps Dendrobium speciosum.
The flowering season of Dendrobium canaliculatum var. canaliculatum is about spring (peaking in September-October) however I hear of reports of wild plants in the northern parts of the range flowering in other times of the year (late Summer, Autumn). Dendrobium foelschei is also reported by FloraNT to flower in the wild in February/April as well as the usual spring season. In my bush house all varieties flower in spring. I do wonder if flowering in Tea Tree Orchids is triggered by a certain pattern in photo-period and that unusual photo-period patterns close to the equator trigger a second flowering season?
Dendrobium canaliculatum var. canaliculatum has been observed to readily form natural hybrids with a number of other Spathulata (Antelope-type) Dendrobiums. It may be that some of the colour variation in this variety stems from gene flow from other species (particularly these) – albeit that the full variation of colour is to be found in specimens that give no other indication of lineage from other species.
The extent of colour variation, and to a lesser extent form variations, in the flowers of variety canaliculatum is impressive. My paltry collection of phone-camera images does not do justice to the range of colours and form in this variety (something I will correct on this website starting with the coming flowering season). I am confident that superior horticultural orchids from both selective breeding within this variety and utilising it in hybrids has much further potential for development. Unfortunately, few growers have true var. canaliculatum in their collections, and even fewer have numbers of plants with the various colour forms. Hopefully these growers will in the future produce seedlings from quality var. canaliculatum parents and distribute them in the hobby so that they can be more widely grown, line bred and used in hybridisation.
A more scientific description of Dendrobium canaliculatum var. canaliculatum (as Cepobaculum canaliculatum) adapted from M.A.Clem. & D.L.Jones, Orchadian 13(11): 486 (2002) can be accessed from the Australian Tropical Rainforest Orchids website by following this LINK.
Dendrobium canaliculatum var. canaliculatum