Dendrobium trilamellatum var. semifuscum
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Dendrobium trilamellatum is a species that has experienced a few reclassifications, similar to Dendrobium canaliculatum. For many years there were two species (Dendrobium trilamellatum and Dendrobium semifuscum). In 1980, semifuscum was reduced to a synonym of trilamellatum. Then along comes Clem and Jones in 2002 and renames them Cepobaculum (instead of Dendrobium) and once again distinguishes the two species trilamellatum and semifuscum.
I will wade in and say that I haven’t seen enough plants across varies locations in the wild to have a confident position. There are clearly populations of this orchid that are significantly (and consistently between the locations) different in plant and flower form. The populations I have seen do fit to the old trilamellatum or semifuscum in their differences. I have not seen enough or looked hard enough at flowers I have seen to work out the extent of intergrading between populations. Furthermore, there are populations elsewhere that I have not observed that may be different again. I have heard that the Dendrobium trilamellatum on some islands in the Northern Territory have yellow flowers, however how the flower and plant morphology compares to the old trilamellatum and semifuscum I have no idea. They are classified by others as var. trilamellatum.
Like most growers (and a few scientists) I do feel that Clem and Jones are overly trigger happy to split existing species into new species. Indeed some of their distinctions I consider unfathomable. For Dendrobium trilamellatum, I am prepared to accept the earlier work that this species encompasses both the form trilamellatum and semifuscum (and nothing from my observations suggests a difference enough to constitute separate species, though this is not always an easy definition to make). Also, the definition as one species is supported by the generally reliable Lavarack & Cribb. But there are clearly wild populations with consistently old trilamellatum features and other populations with consistently old semifuscum features. So I work on the basis of two varieties of Dendrobium trilamellatum – var. trilamellatum and var. semifuscum.
That is a long introduction and this section is about Dendrobium trilamellatum var. semifuscum. Of the two varieties, this is the poorer in terms of horticultural merit. It is found from south of Cooktown (about Archer Point) north to about the McIlwraith and Iron Ranges. I am taking its northern limit from Clem and Jones (2002) as I do not have the field experience to verify this. Certainly, it is found to at least Coen (McIlwraith Range) from my experience.
Across its range Dendrobium trilamellatum var. semifuscum extends well inland into the seasonally dry Melaleuca viridiflora to the top of the dividing range and probably into the western fall as well. The only other Tea Tree Orchid to extend this far inland is Dendrobium canaliculatum. Like Dendrobium canaliculatum it grows rather stunted further inland (canes to about 30cm-50cm) however in better rainfall areas it grows substantially larger (I have seen canes approaching 1 metre near Cooktown). It seems to prefer growing near creeks (on nearly any type of tree) but is found in much lower densities in the stunted forests well away from watercourses as well. In contrast, Dendrobium trilamellatum var. trilamellatum from the plants I have seen in the wild does not appear to grow as large, even though it grows in high rainfall areas. My observations are about 50cm -60cm being the maximum cane length on var. trilamellatum. Clem and Jones (2002) observe differently – they consider var. trilamellatum to be the slightly larger plant of the two (to about 60cm) however perhaps they have not seen the large var. semifuscum plants in the higher rainfall areas.
Canes have varying degrees of black striations but this does not extend to the leaves. Wild plants in poor areas typically only have 3-4 leaves per pseudobulb. Under better conditions and cultivation, the canes can have many more leaves - certainly well over 10 leaves per cane. The leaves are possibly fleshier / more succulent and slightly less broad on average than var. trilamellatum. Plants can grow into rather large clumps with a number of leading growths.
Overall, the differences in the plant forms between the two varieties of Dendrobium trilamellatum are subtle and debatable (to be certain we would really want to see seedlings produced of plants of certain origin grown side by side to maturity under identical conditions). The flowers are where the differences are clear.
Side-by-side image of: (Left) Dendrobium trilamellatum var. trilamellatum; (Right) Dendrobium trilamellatum var. semifuscum.
Compared to var. trilamellatum, var. semifuscum flowers:
The flowers have a delightful and strong scent. A well grown plant of the better versions of Dendrobium trilamellatum var. semifuscum (i.e. flowers are reasonably circular – not too ‘boxy’) put on a great display, particularly when viewed in the right light and distance to appreciate the two-tone effect. There can be many sprays per plant and so there is a great number of flowers, even though each inflorescence will typically only carry 6-10 flowers.
In cultivation both varieties of Dendrobium trilamellatum are about the easiest of the Tea Tree Orchids to grow in my experience. Yes, I grow them identically to Dendrobium canaliculatum under 50% shadecloth.
Many plants of Dendrobium trilamellatum of both varieties have made it into cultivation in Australia over the years and they are reasonably common in the hobby. I believe that they have been flasked quite a few times although it is unknown if these have been of mixed varietal parents within the species (though the importance of this is academic to most). Unfortunately, I have also seen at shows (and in web photos) plants labelled Dendrobium trilamellatum that are clearly of hybrid ancestry. This is not uncommon across other orchids as well (for example procuring a bona fide Dendrobium bigibbum var. compactum is not easy).
Lastly, as to a common name for this species I am at a loss. Most orchid hobbiests simply call them 'trilamellatum' or 'semifuscum'. Possibly the Brown Tea Tree Orchid or Large Tea Tree Orchid would be the most suitable or those that seem to be in use.
As per all these species pages I am referencing a more scientific description of Dendrobium trilamellatum var. semifuscum (as Cepobaculum semifuscum) adapted from M.A.Clem. & D.L.Jones, Orchadian 13(11): 486 (2002) (accessed from the Australian Tropical Rainforest Orchids website by following this LINK). I generally agree with this description however as mentioned in the text I believe that under good conditions this variety grows larger and 'lusher' (more leaves per pseudobulb) than noted by these authors. Their vegetative descriptions fit plants I have observed in the harsher, stunted, Tea Tree forests.