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.
|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.
|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!
|Picture of Nepenthes calcarata sourced from the magical internet. It is possible to see the nests that the plant produces in the tendrils, as well as the "horns" that are very characteristic of this species|
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.
|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).