Tuesday, 2 February 2016

The deceptive world of the bladderwort


Don't be fooled by this picture. Like some orchids, bladderworts produce flowers that mimic a female insect. Or so it seems.

That said, the species I've illustrated here, Utricularia multifida* from Northcliffe in Western Australia, isn't one of the deceptive species so this is a double bluff from me. Sorry. But it does look so pretty en masse...


I've posted before on bladderworts, but it's worth a quick update before I head into the sexually deceptive tendencies of their flowers. These days there are thought to be about 230 species of Utricularia, all them producing small suction traps (bladders) on their roots to catch insects. Like other carnivorous plants (e.g. the Albany Pitcher Plant) the bladderwort extracts nitrogen and so on from the diseased bugs, allowing the plant to live in nutrient-poor soils

The bladderwort flower you are most likely to see in Australia has two small petals fused into knob at the top and the remaining three petals fused into a fringed apron of some kind, leading to their other common name of Fairy Apron or Fairies' Aprons. Utricularia tenella, also found in Victoria, is a good example.

But the flowers of different species vary considerably in size and structure, depending on whether the pollinator is a bee, butterfly, gnat or hummingbird. The flower that interests Polish botanist Bartosz Płachno (who spent some time at the Melbourne Gardens last year) and his colleagues, is that of Utricularia dunlopii from Tropical Australia.


In this beautiful image from Nicole Ribbert's 'Utricularean' site you can see how different the flower is from its aproned relatives. The two long threads sticking upwards are appendages from the upper petals and the three smaller ones from the lower.

At microscopic scale these appendages are covered in glandular hairs, which Płachno says may be involved in production of seductive (to a fly) perfumes. The flowers are hypothesised to be attractive to male flies who cross-pollinate them by attempting copulation first with one flower, then the next, transferring the pollen.

Now the flower of this bladderwort doesn't look a lot like any fly I know, and no one has observed pollination taking place, but the colour and overall form are similar to flowers where 'pseudocopulation' has been proven. Supporting evidence comes from the absence of a nectar reward (that is, there must be some mechanism at work to attract an insect!)

So from this recent work we can't rule sexual deception and pseudocopulation in or out (so to speak) but until someone observes these plants doing their thing in the field we can't be sure.

What we do know (again thanks to Bartosz Płachno and friends) about this and all other bladderwort species is their traps are home to various algae. Here's a stunning picture published last year by ScienceNews showing the artificially coloured contents of a bladderwort trap, featuring at the right-hand side a clump of Maltese-cross and disk-like desmids.


Many of the algae are deceived (or more accurately, sucked in) but it seems that a few at least continue to have happy and productive lives inside the trap. The blue-green algae (Cyanobacteria) - which could fix nitrogen for the plant - seem to be stressed into producing 'akinetes' which are one of the ways they tough out hard times and propagate the species. Not quite copulation, pseudo or otherwise, but yet another complex inter-kingdom relationship involving a bladderwort.

*Note: In the original post I identified the Western Australian species as Utricularia tenella. In a comment added on 6 February 2016, 'quiet1_au' said "I think your Utricularia tenella is actually multifida? They'll always be Polypompholyx to me...". Greg Bourke, carnivorous plant guru at the Blue Mountains Botanic Garden, Mount Tomah, says (on 9 February 2016) "Almost certainly Utricularia multifida. However, Utricularia tenella can produce fairly large flowers, especially around Albany. U. multifida can produce small flowers too, almost resembling Utricularia tenella. With this in mind, you can be forgiven for confusing the two taxa." I didn't even have to beg for it, but all is forgiven!

5 comments:

quiet1_au said...

I think your Utricularia tenella is actually multifida? They'll always be Polypompholyx to me...

Tim Entwisle said...

Could be. I'm certainly no expert in the taxonomy of this (fascinating) group of plants. Thanks!

Greg Bourke said...

Almost certainly U. multifida. However, U. tenella can produce fairly large flowers, especially around Albany. U. multifida can produce small flowers too, almost resembling U. tenella. With this in mind, you can be forgiven for confusing the two taxa

Tim Entwisle said...

Thanks Greg. I have now changed the name in my post. Very glad to get this kind of expert advise! Much appreciated (and you to quiet1_au!).
Tim

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