Dendrobium canaliculatum var. tattonianum
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By far the most common form of Dendrobium canaliculatum in cultivation today is the southern form that is found from about the Daintree area south to the Rockhampton area. This southern variety is most easily distinguished by its flowers – which are consistently a pure white flower with yellow tips to the petals and sepals and purple markings on the throat.
I see this variety regularly referred to as var. canaliculatum – either by including it as the same variety as from northern Cape York or by referring to the plants from north of Cairns as ‘var. nigrescens’ and south of Cairns as var. canaliculatum.
As discussed here the northern form has to be, by convention, Dendrobium canaliculatum var. canaliculatum. If this southern type is a distinct variety – and I do feel it is quite a distinct variety – it requires a different name. The southern form has historically been named as Dendrobium tattonianum before being recognised as the same species as the previously described Dendrobium canaliculatum. Recently Clem and Jones (2002) considering it a separate species: Cepobaculum tattonianum. So I feel the most appropriate name for this plant is Dendrobium canaliculatum var. tattonianum.
Plants of var. tattonianum have a slightly broader leaf than the other varieties and take on a rich apple green colour in good conditions (e.g. in cultivation). A distinguishing feature of var. tattonianum (at least the pure populations south of Townsville) is the lack, or almost complete lack, of dark pigmented edges to the leaves or dark striations on the sheaths on the pseudobulbs. The flower spikes (raceme axis) is often green to red, compared to the almost black of the other varieties. New growths are generally lacking in the red pigmentation of the other varieties.
The flowers of var. tattonianum are relatively consistent in colour. I have never seen or heard of a plant from Townsville south (the purest population) being any other colour than white, with purple on the labellum and yellow tips to the petals and sepals. This colouration is also predominant until about Cairns, although the yellow colour is generally richer - sometimes to the point of being orange. A plant with brown or orange may exist somewhere in the range south of Townsville, but undoubtedly if it does, is exceedingly rare. The white centres on var. tattonianum flowers are always pure, crystalline white. The yellow on the tips stops abruptly, with a relatively clear border before the white centre. Flowers are generally better spaced on the raceme, better presented and of a superior shape than either var. canaliculatum or Dendrobium foelschei. In structure they generally have narrower petals and sepals, a slightly broader mid-lobe to the labellum and poorer substance than var. canaliculatum. Flowers seem on average to be smaller than the other varieties, however there is perhaps more variation in flower size with the largest var. tattonianum flowers larger than the other varieties. Please don’t misunderstand this statement – there are plenty of poor var. tattonianum with dumpy small flowers, hanging their heads in a crowed cluster. There are also plenty of horticulturally excellent var. canaliculatum. Yet on average, var. tattonianum has the best flower form for the show bench.
Dendrobium canaliculatum var. tattonianum flowers. White, yellow and purple with minimal colour variation other than the intensity of the yellow (Right: southern var. tattonianum; Left: northern var. tattonianum).
An average of var. tattonianum racemes in the bush would probably yield 20-25 flowers per spike. I consider a plant with better than 40 flowers per raceme to be excellent and greater than 50 to be extraordinary. I have only seen two plants that can better 60 flowers per raceme (in both cases they could better this quite substantially). One was not my plant - and it had relatively good flowers (probably 70-80th percentile for size and shape). However the spike was very weak and flopped over with the weight of the flowers. The other genuine 60+ flower plant is mine. The flowers on this clone are fine, but only average for size and shape (a 50th percentiler). However the spikes are very strong and straight. Given that one of the most useful features Dendrobium canaliculatum provides in hybridising is its high flower count held well on solid spikes, this clone is a useful parent.
Dendrobium canaliculatum var. tattonianum flowers in spring, with a concentration in September/October but also occasionally a month either side of this. This flowering season is true of cultivated plants and so far as I am aware of all wild plants. Given the observations of wild var. canaliculatum and Dendrobium foelschei also flowering in March/ April, it would be interesting to hear from anyone growing this variety close the equator (e.g. within about 12 degrees from the equator) as to when their's flower.
Intergrading of var. canaliculatum and var. tattonianum
If one were to argue for the inclusion of var. tattonianum as part of var. canaliculatum, part of the evidence would be that the two varieties as I see them intergrade over a very long length of their range. Certainly, I am unable to understand how the plants from Cooktown can be classified as a distinct species to those from Townsville by some authors. Yet, I feel the differences between the two populations are significant and consistent enough in plant and flower form for the use of varietal definitions to be useful. I use the term 'useful' as the definition of what should or shouldn't be defined as a variety is much more debatable than the differences between the populations of these orchids as I have described them in these pages. I personally find it useful to disaggregate the Southern and Northern populations in varietal terms and feel there is enough scope in the general definitions of what constitutes a plant variety to justify doing so.
Whilst the northern limit of variety tattonianum is about Cairns I believe it possible to see traces of var. canaliculatum features in Tea Tree Orchids until about 300km south of Cairns (about Townsville). I have seen a plant just north of Townsville with pale brown flowers, and a number of the plants in this area show varying degrees of dark striations on the new pseudobulbs (a feature that is consistent in variety canaliculatum). At the other end of the range, I have seen a plant in situ in the northern part of Lakefield National Park which was indistinguishable to my eye at the time from any var. tattonianum that could be found around Cardwell (though it should be noted that the other hundreds of plants observed in the same area of Lakefield were classic var. canaliculatum).
Heading north from Townsville, there is a gradual strengthening of the var. canaliculatum features in the wild populations – the yellow on flowers becomes brighter and the dark markings on bulbs become stronger. By about Cardwell to Tully, the yellows are on many plants tend to oranges and by Cairns, brown on a white base becomes reasonably common, the labellums can have some cream and red colouring and the purple disk is often reduced in size. On many plants from around Cairns, even with the traditional variety tattonianum colouration, the yellow can be seen to taper or fade into the white base, unlike the hard, single line change from yellow on the tips to the white centre that distinguishes straight var. tattonianum further south. I apologise for not having photos to show this, though some can be found on the web displaying this. I need to snap a better collection of my own images for future use on this website.
Left to Right: Dendrobium canaliculatum var. canaliculatum; Dendrobium canaliculatum var. tattonianum (northern part of range - intergraded); Dendrobium canaliculatum var. tattonianum (southern part of range).
Along the coastal ranges from north of Cairns to the Daintree flowers are mostly brown and labellums with red, however the shape and presentation of flowers is classically var. tattonianum. These plants were for a time classified as their own variety (Dendrobium canaliculatum var. nigrescens - see HERE) however are now known to be within the var. canaliculatum / var. tattonianum continuum. Inland from the Daintree, between Mt Molloy and Lakeland, strongly growing plants often display long spikes with closely spaced, dumpier flowers of var. canaliculatum in all colours but with predominance of strong shades of var. tattonianum white, yellow/orange and purple on the lip. Only by about the Desailly Range just north of Mt Carbine area across to the Bloomfield River on the coast does the var. canaliculatum form appear most dominant, however plants with some or mostly var. tattonianum colouration extend to about Laura and very occasionally to Cape Melville. Yet on almost all of these plants from north of about the Daintree that appear var. tattonianum, an educated eye can spot features in the flowers that are never seen on plants from around Townsville or further south.
I have attempted to display this intergrading with a stippling of the two varieties on my distribution map here to represent the mix of features from the two varieties across the intergrading zone.
Var. tattonianum plant from Tully Area showing dark features on the leaves and pseudobulbs speculated as arising from gene flow from var. canaliculatum
This range of intergrading is approximately 600km in a straight line. The northern 200km (Cape Melville to McLeod River/Bloomfield River) is predominantly var. canaliculatum, the middle 200km (McLeod River to Tully is all over the shop with var. canalicuatum colours across var. tattonianum forms) and the southern 200km (Tully to Townsville) is predominately var. tattonianum. How to label plants from this range is not clear, however similar intergrading occurs between well recognised varieties of Dendrobium speciosum and Dendrobium bigibbum. Possibly the best solution is to always label plants of known origin with their approximate location of collection (e.g. Dendrobium canaliculatum var. tattonianum (Mareeba)).
Flowers from Cardwell area – flowers are typically heavier in substance and brighter yellows (to pale oranges) than plants from Townsville area and south - speculated as arising from gene flow from var. canaliculatum
A more scientific description of Dendrobium canaliculatum var. tattonianum (as Cepobaculum tattonianum) 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.