Monday, April 4, 2011

An Unexpected Treat (and a little science) - Dendrobium tannii

Back in February, I received a Dendrobium tannii from Plantae as a stand-in for another plant which was not available at the time. It's taken until just the other day to notice that what I thought were oddly spaced leaves were in fact... flowers. The flowers start out green and looking rather "leafy" to my somewhat inexperienced eye. I think the real give-away was when they magically started turning pink...! Closer inspection revealed clearly orchid-esque flower morphology.

Dendrobium tannii in February,
just after being unpacked.
Notice the short canes in the front...
So how does it look now that the flowers are out? Well, those short canes at the front have certainly changed!
Dendrobium tannii flowers
As you can see, they're really packed in there.
No wonder I thought they were leaves when they were still green!
Dendrobium tannii flowers - closeup
D. tannii
Dendrobium tannii inflorescence

Warning for the faint-of-heart - Taxomony Alert!
Dendrobium tannii may not be the correct name for this plant; some people consider this to be a "compact" form of Dendrobium bracteosum, and some refer to it as Dendrobium bracteosum var. tannii. Botanists are constantly revising their opinions of what represents a species within the Orchidaceae and how orchids should best be classified. We can expect a lot of upheavals in "conventional" or "established" nomenclature in the future, particularly as more and more studies using molecular (DNA) information better illustrate the inter-relationships between species, particularly at the generic (genus) level. Of course, this is annoying to hobbyists, but such is life! Many people expect that some of the "mega-groups" (dumping grounds?) like Dendrobium and Bulbophyllum that contain hundreds or even thousands of species will ultimately get broken down into many much smaller genera, with just a few species ultimately "belonging" to that particular genus. Cue wailing and gnashing of teeth amongst growers (and much re-labelling!). I suspect some people will stick to the "tried and true" names for a while, as there can be a lot of flip-flopping when taxonomists haven't quite made up their minds in the face of new ideas and new information. And of course, sometimes you're attached to the old name! (I spent quite a few years as a [fish] taxonomist-in-training, so I appreciate both sides of the argument!). Ultimately, I think it will be good to have an accurate phylogenetic naming/classification scheme within the orchids; I imagine there are quite a lot of polyphyletic and some paraphyletic groups which need to be sorted out. It's going to take some time to get there though, with ~20-30,000 species!

People have managed to cope with the loss of favourite names in science before. The poster child for the rules of taxonomy, at least in Zoology, must surely be Hyracotherium, which could be rather more beautifully referred to as Eohippus, but unfortunately, (if I recall correctly) Owen named its fossilised teeth(!) Hyracotherium long before (well, 35 years before) anyone realised they belonged to a possible ancestor of modern horses, and the rules say the oldest validly published name wins. Eohippus means "dawn horse", whilst the significantly less mellifluous Hyracotherium means "Hyrax-like beast". Amusingly enough, as enamel is so resistant to decay and therefore fossilises relatively easily, palaeontologists (perhaps I read it in one of Stephen Jay Gould's books/essays?) have made remarks about the fossil record of mammals mainly being along the lines of "teeth slowly evolving into different teeth"...

Of course, give it enough time, and the classification will be wrong again - orchids are still busy evolving away (as is everything else!). I have often idly speculated on what will happen to taxonomy and systematics once the living populations have diverged enough from the holotypes, and quite how we're going to reconcile the increasing importance of genetic techniques where holotypes are not amenable to such study... Fortunately, the first half of this paragraph is not something we'll have to worry about in our lifetime, but the second half (matching genes up with holotypes that have irreparably damaged DNA) is going to be tricky. I suspect eventually groups like the ICZN and ICBN will have to establish rules, perhaps some sort of "geno-neotype" ranking - and ultimately, what they're going to do about chronospecies which have arisen within what will then be recorded history!


And now, back to the plants...

Growing-wise, I believe this plant likes things to be a little on the "warm" side and bright light ("Cattleya light" - 2,000-4,000 foot candles); here's what IOSPE has to say about bracteosum:
A small to medium sized, hot growing epiphyte with tufted, erect or pendulous, terete, slender at the base, fleshy and thicker above, to 9 noded, yellowish stems covered in papery sheaths and carrying up to 6 ligulate to oblong, tapering at both ends, coriaceous, rich green leaves that blooms in the spring through fall on 1 1/2" [4 cm] long, pendulous, dense racemes that have fasciculate, ball-like clusters, arising from the nodes near the apex of older pseudobulbs, with 3 to 8, scented, waxy flowers and are found in Papua and New Guinea at elevations of 0 to 700 meters, and is an epiphyte of forest trees and mangroves in rainforests often along rivers and coastlines.
Given the way this plant is growing, I suspect it blooms on "old" canes. IOSPE suggests that bracteosum is fragrant, but I can't smell anything yet; maybe the flowers are still maturing - or perhaps tannii is a valid species, which is unscented (but then again, even within well established species, there are differing degrees of scent...). Culture notes I've read around the place seem to suggest this plant should dry out a little (but not bone dry!) between waterings to prevent root rot.

It's rather fun when your plant's "leaves" turn out to be exuberant pom-poms of flowers! I wonder what other surprises lie in store in my plant menagerie?