The Evolution Of Carnivorous Plants
What makes a plant crave meat?
Carnivorous plants make up less than 1% of all plant species. In total, there are only 800 known carnivorous plants out of over 400,000 plant species documented around the globe. Despite this, culture is obsessed with those rare few that deviate from the norm. The ones that choose insects over soil or thrive in nearly unlivable conditions. Venus flytraps are often sold as exotic houseplants alongside cactuses for curiosity collectors. North Carolina has seen such an interest, that they were forced to make it a felony to poach local Venus flytraps populations.
As with all cases of evolution, somewhere in history, it was beneficial for a carnivorous plant to choose flies. But what were these conditions?
A Role In Evolution
To start, the ability to consume insects or living things has independently evolved in at least 12 different species of plants, known as convergent evolution. This means that even though two plants shared an ancestor, they developed a trait after they broke away from that shared ancestral species. Each species evolved in a different environment to do the same thing, consume living organisms. And while many consume insects, some plants have evolved to consume larger creatures like reptiles, birds, or even rodents.
A Venus flytrap and pitcher plant may both eat insects, but they do it uniquely.
- Pitcher plants use nectar to attract prey, then use a slippery pitcher interior and lid to trap insects inside their pitchers to begin digestion.
- Venus flytraps have unique hairs on the inside of their traps that act like sensors that, when tripped, enclose prey and begin digesting.
Despite looking vastly different, both these structures evolved from leaves and roots. Since carnivorous plants still have leaves, they still take in energy from the sun. The reason they consume meat is because of their root systems.
Roots In The Game
Most live in nutrient-poor environments where a strong root system doesn’t make sense. Carnivorous plants are commonly found in wet areas, such as bogs and swamps, where the soil lacks sufficient nitrogen. There’s no reason to develop a complex, vast root system if the roots aren’t going to find enough nutrients to offset the cost of maintaining and growing the roots to begin with. Instead of strictly absorbing nutrients through their roots, carnivorous plants evolved modified leaves to act as a form of pseudo-roots that take in nutrients by digesting insects.
Carnivorous plants still have roots. However, they dramatically vary across species and serve different functions. Aquatic plants lack roots entirely as they are submerged in water. Xerophytic plants, those living in dry, arid habitats, develop deep and complex root systems thought to access underground water and nutrients.
Others, like Mexican montane butterworts, have temporary root systems that die during the dry winter seasons. In the spring, the rain brings new roots to the butterwort, and large, broad carnivorous leaves form. When the region dries again and approaches winter, these leaves are replaced with non-carnivorous ones.
How Did This Happen?
Evolution doesn’t happen overnight. This was the slow, methodical practice in the same way that fleas evolved to bite dinosaurs, so did plants to eat meat.
Scientists who sequenced the genes of these plants found that the same chemicals used for defense were used to digest and attract insects. The enzyme used by plants to defend against chitin, a polymer used by fungi to make cell walls, was used to digest insect exoskeletons, which are made from chitin as well. Jasmonate is used to regulate plant defensive responses to physical threats, but has been manipulated to trigger traps on carnivorous plants instead. The defenses in a plant’s leaves and root system were simply repurposed.
Instead of generating something entirely new, carnivorous plants changed their existing genes during mutation. This wasn’t a conscious choice, but rather evidence points towards a spontaneous coincidence, where the required combination of traits happened to occur at the same time, instead of any directional selection.
Thankful, there are no reports of a carnivorous plant ever eating a human. Instead, they are adored by collectors and grown to flower and mature on their own.
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