Sunday, January 15, 2017

Blotched Hyacinth Orchid

Dipodium variegatum
 Most of our local orchids flower in spring, but there are a few exceptions. Hyacinth orchids do it in high summer, usually after rain, as with this one which I saw yesterday.

The common name of this plant seems a misnomer to people who know other hyacinth orchid species as well. They are all blotched!

This one is more blotched than the others, though. Notice that the blotches extend to the flower stem (the pedicel and ovary) which doesn’t happen with the others.

It’s always a pleasure to find a hyacinth orchid, as they can’t be grown. They occur only where they’ve planted themselves, and I’ve never heard of one choosing to come up in a garden.
This plant was living in the typical habitat of the species, which is open eucalypt forest with a light grassy understorey. Most of its life is spent completely underground. It only puts up flowering stems once a year, when it’s time to try for babies. A flourishing plant might put up three or four stems.

This flower has its "tongue" hanging out, hoping for a native bee or wasp to be tricked by its bright colours into thinking it will find nectar here so it can be roped into the job of pollination. Like most orchids, it's a cheat. It has evolved to look like a nectar-producing flower, but doesn't make any. It takes a lot of energy to make nectar, and this plant is a miser where energy is concerned. As for which nectar-bearing plant it is imitating - your guess is as good as mine. You do just need to keep in mind that the bees and/or wasps that pollinate this species can't see red.They can, however, see ultra-violet very well, and to them it would look like another colour - something we humans don't have the equipment to imagine. So if we are pondering which look-alike flower the orchids are imitating, the flower shape is probably a better guide. Orchids also often seem to out-compete the flower in question by being larger.  Bluebells, perhaps?

Hyacinth orchids don’t do leaves in any very effective way, from the point of view of being equipped to photosynthetise. (Look closely - they are there, but can't be doing much.) These plants are often described as parasites or saprophytes - the latter meaning plants that get their nutrition and energy from decaying matter under the ground, rather than by photosynthesis.

Saprophytes are not the same thing as parasites. Parasites live on other living organisms. Saprophytes live on plant material which is already dead. They are usually  bacteria and fungi, and are an important part of the growth and decay cycle of their ecosystem, breaking down dead material and making it available for re-use by other plants.

Strictly speaking, hyacinth orchids are neither parasites nor saprophytes. They are myco-heterotrophs, which means that they attach their roots to a  mycorrhizal fungus which is the true saprophyte, living on dead eucalypt roots.  Most myco-heterotrophic plants live in partnership with their fungi. They take some nutriment from them, but also photosynthetise, making carbohydrate which they share with their fungus hosts. Despite their lack of leaves, hyacinth orchids do photosynthise. Those green stems are doing the job. But considering the short life of the flowers, on what is a perennial underground plant, I suspect that the fungus is the partner that does most of the work.
(A few plant species of myco-heterotroph are 100% parasitic. These are the ones that have no green on them at all, such as our local bootlace orchid,  Erythrorchis cassythoides.)

To grow hyacinth orchids, all we need is some land with an open eucalypt forest ecology (complete with its cycle of growth and decay), some relatively open grassland, and the right species of fungus. Nature does it without apparent effort, but we humans have not managed to copy it.

 We have still not invented anything as clever as a plant.


No comments: