Thursday, June 18, 2009

Orchids Do It Differently




Most flowers discretely dust their pollen on visiting insects, but orchids go the whole hog and glue their entire stamens to their visitors. The paired stamens – known as pollinia in orchids - sit inside the hooded upper petal (top photograph) and the nectar supply is hidden deep within the flower, so even long-tongued bees like the one in the second photograph must force their head in to reach it. And that’s when they make contact with the base of the pollinia, which become glued to their head, so when the bee leaves it carries the pollinia with it. By the time it’s reached the next plant each pollinium has split open, exposing pollen that’s dusted on to the stigma of the receiving plant. You can see the white, ruptured pollinia just below the antenna on the face of the bee in the third picture, and the same area enlarged on the final image. Bees are often irritated by having these objects glued to their head and sometimes try to comb them off, but seldom succeed. Why do orchids operate in this way? Well each individual orchid flower can produce hundreds – sometimes thousands – of ovules and it needs a comparable number of pollen grains to ensure that they’ll all be fertilised and develop into seeds – despatching a whole stamen’s worth of pollen in one go, glued to an insect, does the trick very nicely.

9 comments:

  1. Great pictures Phil, to illustrate more knowledge.
    The different variations of how some plants use insects to carry on the generations is fascinating.

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  2. Extraordinary photos, and some fascinating info!
    With such an apparently efficient method of spreading pollen, one wonders why orchids aren't more common.

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  3. Great close shots Phil. It is fascinating the variety of ways flowers have adapted to use insects to pollinate.

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  4. Hi Keith, orchids are particularly fascinating. I've sometimes seen, bur so far failed to photograph, butterflies carrying several orchid pollinia on their proboscis.

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  5. Hi Kingsdowner, I guess it could be because their dust-like seeds are so tiny. Sacrificing an on-board food store for mobility, they depend on the wind carrying them to a suitable site that also contains the fungus that they need to support them after germination. The odds of one of the millions of seeds developing into a flowering plant are probably worse than the lottery!

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  6. Hi John, I'm always surprised by just how long bumblebees' tongues are, and how many flowers hide their nectar in a place where only that long tongue can reach it.

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  7. Truly, wonderful pictures of orchid... I love flowers and plants...

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  8. Orchids are so local because they depend on a fungal partner that relies on certain conditions. That's one of the reasons why they don't transplant effectively.

    Having said that, around 95% of all plants appear to rely - at least in part - on a fungal partner of some kind...trees are an obvious example with their mycorrhizal fungi. And I'm willing to bet if it's 95%, then it will eventually turn out to be 100%.

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  9. Hi Stuart, There's now a lot of evidence that many evolutionarily ancient plants - including liverworts - have mycorrhizal associations so I wouldn't bet against your 100% hunch.

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