What do you think of when you hear the term carnivorous plant? Does it conjure up images of man-eating plants deep within a tropical jungle, perhaps science experiments gone bad, or even Audrey II from the 1960 movie, The Little Shop of Horrors?
Believe it or not, carnivorous (or insectivorous) plants are found on every continent except Antarctica. There are about 800 known species that feed on insects and other small animals. There are 3 major types of mechanisms for trapping prey: adhesive, active, and passive.
- Sundews and butterworts are examples of adhesive traps. These plants have specialized leaves covered in sticky mucilage.
- Pitcher plants have specialized leaves folded into long, slippery channels with pools of digestive enzymes at the bottom. These plants are examples of passive traps.
- Venus flytraps and waterwheels are examples of active traps. These plants have specialized hinged leaves that snap shut when trigger hairs are touched by prey.
Charles Darwin proved to the scientific community that it was possible for plants to be carnivorous. In 1875, he published Insectivorous Plants, summarizing 16 years of experimental research detailing how specialized plant leaves trapped insects and other small animals, digested, and absorbed them. What caused plants to become meat eaters? The evolutionary push for some plants to turn carnivorous may have resulted from their native habitat.
Native Habitats of Carnivorous Plants
Since carnivorous plants are found across the world, their habitats vary widely. They can be found in several areas and grow in a variety of temperatures, from snowmelt streams to tropical jungles. Soil composition can range from acidic bogs to sandy soils to the edges of distressed lakes. These habitats have something in common: nutrient-poor soil lacking inorganic nitrogen, phosphorous, and calcium. Plants need these essential nutrients to thrive.
Adaptation, Structure, and Function
Tanya Renner, an evolutionary biologist at Penn State, has found that carnivory has evolved many times over the millions of years that flowering plants have been on earth. She has documented that the adaptation to obtain all nutrients from specialized leaf structures instead of roots has appeared independently at least 12 times, and in different places.
While the adaptations that have made carnivorous plants successful are well documented, until recently, the genetic mechanisms for the changes have not been clear. In 2021, Rainer Hedrich, of the University of Wurzburg, Germany, used DNA sequencing to identify genes associated with carnivory. His findings point to co-option and repurposing of genes found in many flowering plants. Researchers used techniques from the fields of genomics, transcriptomics, and proteomics to isolate the genes that are switched on in carnivorous plants and which proteins are needed at mealtimes.
In the 1970s, researchers studying the digestive fluid in traps of carnivorous plants discovered that the fluid contained enzymes that functioned like many of the chemicals that plants use to fight off harmful bacteria, fungi, and insects. The enzymes found include chitinases, proteases, and purple acid phosphatase, which enable plants to break down insect exoskeletons and proteins and extract usable phosphorus. All these substances perform protective functions in non-carnivorous plants. This supports the view that co-option is driving evolution.
Genomic studies of carnivorous plants have yielded many fascinating findings about how and why plants became meat-eaters. To find out more about this, check out the sources cited below. Even if you can’t conduct genomic studies in your classroom, you can directly observe these insect-eating plants and examine some of the leaf and digestive adaptations that place these plants in a unique category.
Carnivorous Plants to Study
Purple pitcher plant
Sarracenia purpurea. The leaves are hollow, pitcher-shaped, and often dark red blotched with green; they are intricate trapping mechanisms capable of luring, trapping, and digesting many insects.
Venus Flytrap
Dionaea muscipula. The most spectacular of the carnivorous plants. Prey is captured in a 2-sided, clamshell-shaped trap. Insects are attracted to the trap by nectar secreted from numerous glands around its edges, and possibly by its bright coloring. The trap closes rapidly when the prey stimulates small trigger hairs on each half. Glands lining the resulting pouch then secrete digestive juices which consume the insect; the trap reopens within 3 to 5 days. Flytraps are best grown in Sphagnum moss in acid-bog terraria.
Sundew
Drosera. Small rosettes of reddish leaves, each bearing numerous glands topped with tiny droplets of sticky fluid resembling dew drops. Gnats and tiny flies stick to this “dew” and are digested by the plant. Good for acid-bog terraria.
Butterwort
Pinguicula. Small rosettes of yellow-green, butter-colored leaves with microscopic, mucilage-producing glands. Gnats and other small insects are trapped on the leaf surface. Does well in bog terraria, but needs good drainage.
Carnivorous Plants for the Classroom
With the proper care, carnivorous plants can be grown in the classroom. We provide several options for observing and studying insectivores with students.
Includes pitcher plant, Venus flytrap, Cape sundew, live Sphagnum moss, 4-L vessel, soil, and instructions.
Set includes Sphagnum, bog plant (our choice), pitcher plant, 2 sundew plants, 2 Venus flytraps, and soil.
Includes a purple pitcher plant, Venus flytrap, sundew, and butterwort. Carnivorous plants should be maintained in a small terrarium or other suitable environment.
Caring for Carnivorous Plants
We offer care guides to help you set up and maintain your carnivorous plants. The guides provide valuable information, including the amount of water, sun, nutrients, and temperature range the plants need to thrive. The Carnivorous Plant Care Sheet will provide the information you need.
Carnivorous plants are a novel way to study structure and function and natural selection. With the groundbreaking genetic work used to decipher the genes responsible for successful carnivorism in plants, students can trace the evolution of carnivorous plants while observing the plants’ adaptations. Count on Carolina for exciting ways to enhance and update your biology curriculum.
Sources
“Carnivorous Plants.” The San Diego Zoo Wildlife Alliance. 2022. https://animals.sandiegozoo.org/plants/carniverous-plants
“Carnivorous Plants.” The Botanical Society of America. https://botany.org/home/resources/carnivorous-plants-insectivorous-plants.html
Lotzof, Kerry. “Carnivorous plants: the meat-eaters of the plant world.” https://www.nhm.ac.uk/discover/carnivorous-plants-meat-eaters-of-the-plant-world.html
Pain, Stephanie. “How Plants Turned Predator.” Knowable Magazine. March 2, 2022. https://knowablemagazine.org/article/living-world/2022/how-plants-turned-predator
