Scientists and laypersons alike,owe so much to Charles Darwin. Collective fascination with carnivorous plants dates to 1875 when he published a book on insectivorous plants, as he named them. As he wrote in his autobiography, ‟The fact that a plant should secrete, when properly excited, a fluid containing an acid and ferment, closely analogous to the digestive fluid of an animal, was certainly a remarkable discovery.‟
Darwin was pleased that nature offered him such a handsome instance of convergent evolution. Indeed, the pouches that plants in the Nepenthes genus use to first trap and then digest their prey resemble a mammalian stomach like ours, size included, they are up
to 25-30 cm long.
The topic of carnivorous plants reminds me of the justly famous scene in the movie Drôle de drame (1937) in which the Michel Simon character — who plays an all-too-conventional scientist — duly daily feeds his favorite plant : ‟une mouche, deux mouches,
… one fly, two flies, …‟ .
Carl Linnaeus gave this plant its name, in 1737 in the treatise Hortus Cliflurtianus. Drawing on classics from antiquity, Linnaeus chose to refer to an episode in the Odyssey: in the fourth book (4, 219-233), Ulysses’s son Telemachus is urged by the goddess Athena
to go search for his father, who has yet to return from Troy to his home in Ithaca. Telemachus’s first stop is in Sparta, where he is hosted by king Menelaus and his wife Helena. At seeing Ulysses’s son, Menelaus is reminded of the Trojan War which greatly saddens him, and the whole gathering becomes overcome by grief. At which point Helena serves everyone a soothing drink she has learned to mix — consisting of nepenthes (opium possibly) into wine — during her previous stay in Egypt with King Thonis.
The Swedish naturalist was thus being ironical about the last moments of trapped insects, being lulled into sleep. But what about the full name of the plant featured here? Nepenthes rafflesiana was discovered by Dr. William Jack in 1819. He thus wrote in Curtis’s Botanical Magazine:
‟It is impossible to conceive anything more beautiful than the approach to Singapore, through the Archipelago of islands that lie at the extremity of the Straits of Malacca. Seas of glass wind among innumerable islets, clothed in all the luxuriance of tropical vegetation and basking in the full brilliance of a tropical sky...
I have just arrived in time to explore the woods before they yield to the axe, and have made many interesting discoveries, particularly of two new and splendid species of pitcher-plant.‟
He named the first species in homage to Thomas Stamford Raffles (1781-1826), the founder of Singapore, who would also leave his name to a famous hotel built there in 1887. Raffles was also an amateur botanist of distinction.
The Nepenthes genus fields nearly 150 species among tropical regions from Madagascar in the East to Pacific islands, with their majority in Southeast Asia. Borneo hosts the greatest number of Nepenthes species. Others in the same general area, in New Caledonia for instance, may have originated in Borneo. Dissemination by birds is likely.
Nepenthes are vines or shrubs that bind to adjacent plants with tendrils that develop from the leaves tips. The common name for Nepenthes is pitcher-plant, the pitchers being the stomach-like vessels used for both trapping and digesting insects and other
arthropods.
There are two kinds of pitchers, both modified leaves. Young plants grow rosettes of lower pitchers, while adult plants grow upper pitchers. The lower pitchers touch the ground. The upper pitchers are aerial. Accordingly, the two kinds attract and kill different insects, creeping and flying respectively. Typically, the non-fragrant lower pitchers attract and devour ants, providing them with about 70 % of the foliar nitrogen. The fragrant upper pitchers are meant for larger insects.
How are these animals thus lured to their deaths ? By a number of seductive devices: highly visible (to insects) color patterns; emission of seductive fragrances and of carbon dioxide; and of course nectars, akin to those of flowers but in this case produced from extrafloral nectaries placed at the rim of the pitchers.
Once an insect gets into a pitcher, it is trapped. From the inside, the rim is slippery and does not offer a grip. Overhanging guard cells deny traction to the claws. Wax crystals clog the claws. The invertebrates are frustrated in their attempts at escape. The inevitable result is fall into the digestive fluid inside the pitcher. It is highly viscoelastic, binding the prey until it drowns and becomes digested.
Evolution has perfected these carnivorous plants, no wonder that they thrive in their widespread ecological systems!