Probably the
most interesting group of plants for the majority of people are the carnivorous
plants because of their behaviour with insects. Wait, because of the insects’
behaviour with these plants! Well, in any case we must all agree that
carnivorous plants were a wild invention of Nature.
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| Different growth stages of pitchers in the QBG carnivorous plants glasshouse |
My opinion about them
became even wilder when I found an old article about a Bornean pitcher plant (Nepenthes bicalcarata), which
relationship with insects is absolutely unexpected for a carnivorous plant. So first,
let me remind you some aspects about the biology of these plants: pitcher
plants are known by getting nutrients from insects as a supplement. Their
strategy is to attract insects using a trap, a modified leaf (the pitcher),
which is full of enzymes and digestive liquid where the nutrients can be
absorbed.
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| In Nepenthaceae, the leaves are differentiated into pitchers and the petioles are the photosynthetic part of the plant, having the function of the leaf but not being a true leaf |
The insects are attracted by the extra-floral nectaries and often
fell in, drowning in the fluid. However this particular species, Nepenthes bicalcarata, nests ants (Camponotus schmitzi) in
their swollen and hollow tendrils. Strangely, these ants forage on the inner
side of the pitcher, crawling over the slippery walls without difficulty and
even swimming in the pitcher fluid to forage and feed on the insect prey’s of
pitchers. So, what is the advantage for the plant on having other insects eating
the food that they get alone by using their own pitchers? The ants only collect
large prey insects – all the other small insects are digested and absorbed by
the plant. Big preys take long time to digest, and this would end up on putrefaction
and rotten pitchers, which is obviously something not very healthy for a
pitcher plant to have. So these pitcher plants get rid of the large preys by
offering them to their friends - ants. “Wow!” – I can hear you guys whisper. No
worries, I whispered the same – these plants are really something!
Even though this
is all undoubtedly very interesting, the flowers of Nepenthes do also tell a story. Nepenthaceae, as all the members of
Caryophyllales order have no petals, so their perianth has only one single
whorl made out of sepals. The flowers are also easily recognizable by being
dioecious (meaning that sexes are separated in different flowers, male and
female) and tetramerous. Of course that a carnivorous plant also needs insects
for pollination, so they do produce a lot of nectar to attract a lot of
insects. Some will end up in the pitcher-insect-hell, but others will end up
licking the sepals which are fully loaded with sweet nectar. It’s a matter of
luck for insects I suppose.
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| Typical inflorescence of Nepenthes, a racemose with paired tetramerous flowers, each one subtended by one bract |
Another very
interesting fact about the Nepenthes are
the male flowers, which have all the stamens (ranging usually from 4 to 24 in
number) fused together in a structure which botanists decided to call “synandrium”
(syn meaning fused and andrium referring to the male part).















