CLICK ON THE IMAGES ABOVE TO EXPAND AND VIEW
It may difficult to understand today, but until 1982 this species was considered a colour variety of Dendrobium canaliculatum. Still called the Pink Tea Tree Orchid, this species does appear superficially similar to Dendrobium canaliculatum, but is also distinctly different.
Plants of Dendrobium carronii are similar to Dendrobium canaliculatum, however generally smaller in size. The leaves are slightly broader, and have an even purplish tint with minimal dark margins to the leaves or dark striations on the pseudobulbs compared to Dendrobium canaliculatum var. canaliculatum. Dendrobium canaliculatum does grow into larger clumps under favourable conditions in the wild, however Dendrobium carronii seems to persist as only a few leading growths.
The flowers of Dendrobium carronii are highly distinct. The sepals are mostly white, and much shorter than the petals. The labellum is solid yellow to green. The petals, much longer than the sepals, are a dark glossy maroon colour and have minimal twisting (a half twist is typical). In bud, the tips of each individual bud point straight to the sky, regardless of the habit of the inflorescence. They only move to a horizontal position just prior to opening. Flower size is probably a fraction smaller on average than Dendrobium canaliculatum, however the colouration, strongly erect petals and tiny plant size means the flowers make quite a visual impression.
Dendrobium carronii flower buds showing the upright 'toothbrush' effect of the flower buds. Just before opening, the buds will re-position themselves to a horizontal position.
In the wild, Pink Tea Tree Orchids are found on the East Coast of Cape York Peninsula (North of about Cooktown) and into the Torres Strait and southern Papua New Guinea. Records from Papua New Guinea (according to Orchids of New Guinea) are from the Daru area (directly above the Torres Strait) as well as the Port Morseby area. In Australia it does not extend into the drier zones as does Dendrobium canaliculatum and Dendrobium trilamellatum var. semifuscum, however still favours highly lit and breezy locations in the higher rainfall regions. It is reported to grow to moderately high altitudes (700m) in both Australia and New Guinea.
Dendrobium carronii is apparently quite common in some localities, however I have not seen many plants in the wild. After scouting Melaleuca viridiflora forests in a number of suitable-looking locations with no luck, I was surprised to find my first colony growing almost into the twigs on fibrous-barked Eucalypts. The location was on the edge of a dried up waterhole. There were no Dendrobium canaliculatum in the general area, although Dendrobium johannis and Dockrillia rigida grew on various hosts (including Melaleuca viridiflora) in the denser patches nearby.
I feel somewhat fraudulent writing about the cultivation of Dendrobium carronii as my experience is limited. Dendrobium carronii has a reputation with many as extremely difficult to cultivate (perhaps more difficult than Dendrobium canaliculatum). I did cultivate and flower a couple of seedlings for about three years until they were killed during a period where I was regularly away for work (and the spouse accidentally turned off the automatic watering). These were grown mounted on a mesh tube filled with LECA and grown under 70% shade (this is relatively high shade for this group of orchids). I do not recall any particular difficulties with their cultivation. Recently I have managed to acquire several new small plants, and these are growing in 100% perlite exactly as I cultivate Dendrobium canaliculatum. Whilst they are relatively slow growing and still in the adaptation phase (most plants suffer reduced growth at first under my cultivation regime until they are adapted) they appear to be doing well compared to where I would expect Dendrobium canaliculatum or Dendrobium johannis at a similar stage of transition. I have some plants under 50% shade and others under 70% shade. They are watered (with fertiliser injected every watering) three times a week year round as are all my orchids.
An interesting article on deflasking and growing Dendrobium carronii from Singapore can be found HERE. The technique is different to that I would use, however it clearly works.
The Pink Tea Tree Orchid is not common in cultivation, certainly not in Australia, however its rarity means that it is generally treated with a bit more respect than Dendrobium canaliculatum. The species does seem to be more prevalent in cultivation overseas, possibly as common as Dendrobium canaliculatum (which to be truthful does not appear to be all that common in its species form). It can certainly be cultivated successfully, and deserves to be grown more. In Australia, I am aware of one breeder who now has three different bloodlines of Dendrobium carronii in flasks, so hopefully with increased supply in the future more will attempt to grow this species.
A more scientific description of Dendrobium carronii (as Cepobaculum carronii) 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.