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An upside down orchid

August 17, 2011

In many cases orchids have fairly restricted ranges. Some are endemic to Thailand (such as Chiloschista viridiflava), some are only found here in the north and in adjacent countries with similar monsoon forests (such as Seidenfadenia mitrata), some are only found in Southeast Asia (such as Vanda denisoniana).

On the other hand, there are orchids such as Calypso bulbosa which are circumboreal, i.e. you can find it Scandinavia (although rarely now due to habitat destruction), Japan and North America. In a previous blog we discussed why epiphytic orchids never made it to Europe, and in another blog I mentioned that some ornamental orchids have been introduced and naturalized elsewhere.

On the 16th of August I photographed the blossom of a native Thai orchid which also occurs in Africa and South America: ‘The greater yellowspike’ (Polystachya concreta, Orchidaceae). The genus Polystachya (meaning ‘many spikelets’) with some 150 species is largely African, and this species is hitherto the sole representative known in Asia. Being one of the most widespread orchid species in the world, it is not endangered unlike so many other Thai orchids.

Although the literature claims it has no horticultural value, I must say I was enchanted by its decorative, erect, yellow spike with its peculiar buds, and when the flower unfolded they looked like little girls with long blond hair. The specimen of the Orchid Ark grows on a branch together with Vanda flabellata. This species is known to grow in dry environments on dipterocarp branch ends. Since I do not know much of the background of this branch with its two orchids, other than it was donated to the Orchid Ark, I think we dare to restore it to a Dokmai Garden Dipterocarpus tuberculatus tree. If anyone would like to study this little wonder, now is the time!

The flower is strange! From a picture you do not grasp what you are looking at. I had to use a nail scissor and carefully detach a stiff (‘concreta’) flower to study it with a 20x dissecting microscope. It turns out, this is an upside down flower! Most orchids are resupinate, meaning they have the lip below the column. In this case, the flower is not resupinate, i.e. the lip is on top. What you see on this photograph are the sepals unfolded like a blond girl’s hair, exposing what is normally the underside of the lip. (Unfortunately I have no camera attached to that microscope).

Here I hold a detached flower upside down, and then it looks like a ‘normal’ orchid with the column at top. Why would an orchid flower grow upside down? We can only hypothesize. Maybe the pollinia were better protected on the lower side of the pollinating insect rather than being attached to the eyes, head or thorax which is more common? Perhaps the pollinating insect kicks around a lot, and so firmly trample the pollinia into the stigma, the female part? Apparently this flower trait became superior in the orchid’s reproduction so that upside down flowers resulted in more seedlings than in plants with normal flowers, and this original mutation has so far resulted in a genus of 150 species. Why are there not more of them in Asia? We do not know when the mutation occurred. Nothing in nature in fixed, the environment is continuously changing and mutations occur all the time, and so Polystachya concreta might be the first scout of its genus to the Asian continent, not yet found in New Guinea or Australia.

Text & Photo: Eric Danell

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2 Comments leave one →
  1. allan docherty permalink
    August 17, 2011 9:32 AM

    As usual Eric, very interesting and informative.
    Keep up the good work.
    Regards,
    Allan & Heather

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