Plants are mostly autotrophic that produce food by photosynthesis from inorganic raw material like sunlight and carbon dioxide. However, there is a very special group of plants that evolved in a unique way that they obtain nutrients through trapping animals. Unlike parasite plants who are unable to photosynthesis, carnivorous plants are capable of making their own food by photosynthesis and meanwhile capable of eating animals. As sessile and passive forms of life, how do carnivorous plants become so aggressive and differ from “normal” plants?
There are about 600 species of carnivorous plants. Most have specialized leaves structures that evolved into trapping mechanisms. They capture mainly insects, which they digest slowly with digestive juices. Carnivorous means flesh-eating. Carnivorous plants were termed as insectivorous plants during Darwin’s time somehow is not very accurate and limiting. Some species had evolved to eat small animals such as snails, spiders, tadpoles, frogs, lizards, rats, and small mammals at a very rare event. Therefore, carnivorous in general is more accurate. Other plants like petunias, potato, rhododendrons, and teasels do catch and kill insects as well. However, they did so to protect themselves for defense purposes. They might obtain some nutrients such as mineral or trace elements from the natural decayed bodies, but their primary mineral uptake is performed by roots from the soil.
A typical “normal” plant absorbs water that contains minerals from the soil through their roots. In another word, the soil is normally enriched with nutrients. Whereas carnivorous plants grow in wet and mineral-deficit substrates, which normally are in a severe shortage of nitrogen, phosphorus, and potassium. A “normal” plant may survive on such conditions for a period of time, but it definitely would not be able to produce flowers, seeds, or offspring.
As sessile creatures, plants have to deal with their environments, no matter fertile or barren by adjusting themselves. Carnivorous plants have been very successful in terms of adaptation to different environments. They use various strategies to trap their prey. About half of the species capture by aspiration, the animal is sucked into a small sac, where it is digested. Others would lure, catch or trap, kill, then digest the prey. About one-third trap their victims in mucilage which is viscous nectar that the insect becomes stuck. They obtain the nutrients through the moving packets of minerals and nutrients from animals that have legs and wings. The digestion usually involved digestive enzymes and acids that dissolve the victims into a palatable form. Some species such as Darlingtonia and Heliamphora are examples of pitcher plants that do not produce actual digestive enzymes and rely on bacterial action to dissolve their prey.
Carnivorous plants are fantastic by their stunning appearance and varieties of colors, sizes, and shapes, which is reasonable for being attractive for luring purposes. However, it’s a trade-off characteristic for pollination because the pollinators might get trapped and killed as well. Therefore, they developed different mechanisms to overcome this challenge, kind of living a double life by using different timing, physical location, and pollinator section. They produce the flowers only when the traps are not functional. They produce a very long flower stalk that is away from the specialized leaves to avoid the pollinators get trapped while pollinating the flowers. The pollinator section is distinctly different from the traps whereby the flowers produced will be in bright colors such as white, pink, or purple to attract the pollinators. It seems carnivorous plants are so “intelligent” in calculating these amazing strategies. As one of the most popular characters in scary and sci-fi movies, they are also very successful at attracting human and luring curiosities.
However, are they really capable of eating large mammals, such as humans? The answer is not yet as long as the animal can learn and escape. No matter how sophisticate the traits are, the function and appearance of plants are defined and shaped by their environments with the tendency to maximize the usage of resources surrounded by them. In order to evolve such kinds of traits, these resources have to be regular and stable, remaining steadily available for several million years, in a way similar to that of light, air, and soil. The soil is nitrogen-poor ground that is acid and marshy, but alternative resources such as small insects flying around that carry nitrogen are quite regular and stable in wet and warm conditions. Besides insects are not capable to learn and escape, will fall into the same trap again and again. Intelligent animals such as monkeys, on the other hand, will learn from mistakes, memorize the danger and thus avoid such traps.
Carnivorous plants can be further categorized by their habitats into aquatic, semi-aquatic, and land plants. Charles Darwin once wrote that he care about Drosera, one of the largest genera of carnivorous plants than the origin of all the species in the world. Some carnivorous plants are now classified as endangered species due to deforestation for human activities like housing, agriculture, collections by hobbyists and collectors, change in climate, and slow-growing in nature. However, thanks to plant tissue culture technology, most species can be propagated and multiplied in labs to conserve the germplasm. In an era of biotechnology blooming time, precise DNA editing, genomic rearrangement, together with artificially intelligent, machine learning, and other technologies. Will that allow manipulations and creations of desirable phenotype in plants becoming reality? Maybe not yet, however it does create a space for imagination to soar.
Further readings:
Charles Darwin (1875). Insectivorous Plants
Adamec, L. (1997). Mineral nutrition of carnivorous plants: a review. The Botanical Review, 63(3), 273-299.
Temple, P. (1988). Carnivorous plants.
Pietropaolo, J., Pietropaolo, P. A., & James. Pietropaolo. (1999). Carnivorous plants of the world. Timber Press.
Meyers-Rice, B. (2006). Growing carnivorous plants. Timber Press.
Jennings, D. E., & Rohr, J. R. (2011). A review of the conservation threats to carnivorous plants. Biological Conservation, 144(5), 1356-1363.
D’amato, P. (2013). The savage garden, revised: Cultivating carnivorous plants. Ten Speed Press.
