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Dendrobium johannis is perhaps the most popular of the Tea Tree Orchids in cultivation in its species form (Dendrobium canaliculatum has been utilised much more for hybridisation). I don’t hear it referred to by a common name much, but Chocolate Antelope Orchid would be the one I come across the most.
Before I get into any else I want to clear up one thing. There is much reference in catalogues, on the web and in writings of a variety of Dendrobium johannis - var. nigrescens. Certainly some plants of Dendrobium johannis are very dark – almost black in the right light. However I am not aware of any scientific description of a distinct variety of Dendrobium johannis. Whilst my information is far from complete, from my readings and observations of wild and cultivated plants I find no evidence that there are any separate varieties of Dendrobium johannis to be described. Some plants in any population are darker than others, however this does not constitute a variety (see my discussion of ‘Dendrobium canaliculatum var. pallidum'). I am not even personally comfortable calling dark Dendrobium johannis ‘forma nigrescens’ as the darker plants appear as a continuum of shades in a population, rather than a distinct colour morph. So please, if you have a special dark Dendrobium johannis give it a nice clonal name (e.g. Dendrobium johannis 'The Dark Side') rather than persisting with falsely assigning it as a variety.
Unlike canaliculatum and carronii this little orchid grows an upright ‘cane’ like more traditional Dendrobiums. The canes are fusiforme (i.e. swollen to the centre) and not all that tall. 20cm would be about the average cane height for a mature plant with about 30cm the maximum. Each cane has 3-5 bright green leaves, which are thin and succulent, but much broader than Dendrobium canaliculatum. The sheathes of the leaves over the cane have dark blackish striations – on some plants parts of the cane can appear almost pure black, but no dark colouring extends to the leaves. Like Dendrobium caronnii, Dendrobium johannis does not tend to grow into thick clumps, and it is rare to see more than two or three leafed growths in a plant either in the wild or in cultivation.
Flowers of Dendrobium johannis have a wonderful glossy appearance being a dark brown to blackish brown with a faint purplish undercoat. Very dark plants in particular almost appear to have been lacquered. Flowers open widely and are a little larger than the average Dendrobium canaliculatum being perhaps 30mm to 40mm across. The labellum is bright yellow and most plants have a purplish spot right on the tip of the labellum as well as over the pollen cap. Flower count is to about 15 or 20 on the very best plants but usually less. Flower spikes can either be straight upright or flop over with the weight of the flowers. The flowers have a strong scent during the day, that most describe as unpleasant. I do not personally find the scent unpleasant, although it is powerful and a little unusual.
Unlike all of the other ‘Tea Tree Orchids’, Dendrobium johannis is primarily an Autumn flowerer. Mine are in flower March and April. Some of the plants from the northern parts are reported to flower in Spring. These plants flower in late winter/early spring in cultivation - so the flowering is seemingly genetically determined. Other characteristics of the plants and flowers appear without difference to typical autumn flowering Dendrobium johannis. I do wonder if a spring x autumn flowering Dendrobium johannis would give the possibility of a twice yearly flowering plant?
Dendrobium johannis is found on Cape York Peninsula on the east coast north of about the Stewart River and Coen. It extends into the Torres Strait and southern Papua New Guinea, where (according to Orchids of New Guinea), it is thus far recorded from a relatively limited area directly above the Torres Strait (Mari and Morehead areas).
I have always found this species growing in more open areas adjacent to rainforest. The highest densities I have observed were on the lower branches (still 20m-30m above the ground) of huge, fibrous-barked Eucalypts in wet sclerophyll forest adjacent to rainforest in the Iron Range (near Lockhart River). This forest did not look too dissimilar to that you might see on the sides of mountain gullies around Brisbane or Sydney. It also grows on Melaleuca viridiflora and other smaller scrubby trees but again in the higher rainfall areas and in my experience, close to (but not within) rainforest areas.
I grow my johannis in the same way as Dendrobium canaliculatum (see the Culture section HERE) – which is about how I grow all my orchids! I find it a relatively easy species to cultivate although they a relatively slow growing species (slower than all the other Tea Tree Orchid species except perhaps Dendrobium caronnii). It has no problem with a bit more shade than the other species and about 70% shade in my climate seems perfect for growth and good flowering.
Dendrobium johannis is a very good parent in hybridising, often contributing intense colouration without, surprisingly, overwhelming the other parent. For example in Dendrobium Minnie (johannis x carronii) the purples of the carronii are enhanced, whereas in many other hybrids carronii tends to have its colouration washed out. In Dendrobium Our Native (speciosum x johannis) johannis is able to provide enough strength to the rather dominant speciosum parent to produce good gold and caramel colours on flowers with a gentle twist.
A more scientific description of Dendrobium johannis (as Cepobaculum johannis) 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.