by Jen Karberg, Research Program Supervisor
Plants are remarkable at adapting to their environments and finding a way to survive in a seemingly impossible place. Carnivory in plants, the ability to consume insects and other organisms for necessary nutrients is one of those incredible adaptation. Carnivorous plants can seem exotic but you might be surprised to find we have some of these plants right here on Nantucket.
Carnivorous plants are one of the more unique adaptations seen in the plant kingdom. These plants are typically found living in places where, for a variety of reasons, they have a hard time getting the nutrients they need for healthy growth – which is a ready supply of nitrogen and phosphorus.
There are a variety of nutrient-poor kinds of habitats and here on Nantucket, we find carnivorous plants living in some of our more isolated wetlands. These wetlands are called bog or poor fen wetlands and are characterized by their hydrology, where their water comes from, which in turn controls which nutrients are present and available for plants. Bog wetlands typically only get their water from precipitation with very rarely any groundwater. This is important because groundwater will often contain nutrients it has picked up by moving through soil but precipitation typically has very little nutrients in it, the water is mostly sterile. Additionally, the soil in bog wetlands is actually purely organic and made up of a moss called Sphagnum in various stages of decomposition. This decaying Sphagnum moss creates soil called peat and it doesn’t have nutrients that are available to other plants.
This means that plants growing in bog wetlands need to be adapted to lower amounts of nutrients. We actually have quite a few of these wetlands hidden around the island, remnants of the glaciers that once moved over Nantucket. The most well known and easy to find bog on Nantucket is Donut Pond in the Middle Moors. It’s easy to find but not easy to access though as it is surrounded by a deep moat of water. In the center of the Pond, a bog wetland thrives!
So what is our cast of carnivorous plants on Nantucket? The largest and showiest is the Northern Purple Pitcher Plant (Sarracenia purpurea).
The leaves of the pitcher plant are modified so they formed closed pitchers. Each pitcher has a lid with a nice smooth surface, containing nectary glands which attract insects to the plant. When insects stop to taste the nectar treat, they slip and tumble down into the pitcher. The inside of the pitcher is covered with small downward pointing hairs so insects are unable to easily crawl back out and instead they slip down to the bottom of the pitcher which is filled with water and a whole suite of microorganisms whose job is to breakdown and digest the insect meal. Once the insects are digested, nitrogen and phosphorus can be absorbed right into the pitcher wall and used by the plant.
The pitcher plant is long lived, usually up to 25-30 years and each year they produce 2-3 pitchers over the course of the growing season. Once a single pitcher has had 4-5 meals, it doesn’t work as efficiently and the plant produces more. Interestingly, the plant still needs to photosynthesize to produce energy for plant growth and will adapt it’s leaves depending on nutrient and sun availability. When pitcher plants are shaded out – they grow smaller pitchers with larger pure green leaf area to capture more sun rays. When the plant is out in the open, the pitchers get larger and redder to maximize insect capture. This is one of the more fascinating and widespread pitcher plants, growing from northern Canada all the way down to the Gulf Coast.
The second most common carnivorous plant on Nantucket is the sundews (Drosera ssp) and we have a few different species here. These diminutive plants grow next to and around the pitcher plants but they can often be much harder to find.
Sundews produce carnivorous leaves covered in tasty smelling, but very sticky nectar glands. When an insect, such as an ant, wanders across these leaves they get instantly stuck. The leaf is then triggered to roll up around the insect and the plant begins secreting digestive enzymes. Like with the pitcher plant, nutrients from the digested insects get absorbed right through the leaf and are used to help plant growth. The sundew produces lovely delicate little flowers, often white or pink during the spring, making these small plants a little easier to find.
The final carnivorous plant we find here on Nantucket is the bladderwort (Utricularia ssp.) and this is the most difficult to find and unique carnivorous plant we have. Bladderwort plants are impossible to find unless they are flowering which usually happens for just a few weeks in the spring. Bladderworts send up short delicate stalks with a few small yellow flowers and this is the only aboveground structure the plant has, most of this plant is living entirely below the soil surface.
The carnivorous parts of the bladderwort are located entirely belowground and consist of small (~0.5-1cm) sized bladders located all along the plant roots.
These little bladders have a small valve opening covered in sensitive hairs. When microorganisms swim too close to the hairs, the value opens and sucks in the microorganism. Once it’s trapped inside the bladder begins digestion allowing nutrients to get absorbed into the plant.
Check out this amazing and informative YouTube video showing these microscopic bladders in action.
The plant world is filled with all kinds of marvelous adaptations to stressful living conditions. What is your favorite plant adaptation?
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