Solving Problems The Pitcher Plant Way

This writeup will be appearing in the Fall 2024 newsletter from the Community Lakes Association (www.communitylakesassociation.org).

Plants have a rather obvious problem. They're rooted in place. They can't move. Being stuck in place has a profound impact on every aspect of a plant's life, from how they grow, to how they store food, to how they reproduce and spread their seeds. 

One less-obvious problem involves nutrition. Plants are solar-powered. They use sunlight energy to combine water and carbon dioxide into glucose. Glucose, in turn, is used both as an energy source (just as it is in animals), and as a precursor to making structural molecules such as cellulose. Plants need more than just carbon dioxide and water, however. They also need nutrients such as phosphorus, iron, potassium, and nitrogen. These are used to create proteins, DNA, enzymes, and a host of other essential molecules (just as they are in animals).

Plants usually obtain these nutrients from the soil. The availability of soil nutrients influences which plants can grow where. Boggy, acidic soils - common around the waterlogged edges of ponds in Maine - tend to be particularly low in nitrogen. 

So what's a bog-growing plant to do? It's stuck in place. It can't go searching for nitrogen elsewhere. Some plants have an ingenious solution. They 'order in' their nitrogen from afar, tricking insects into bringing this nutrient right to them. Unfortunately for the insects, their bodies store the nitrogen that the plant seeks. These are the carnivorous plants.

Maine hosts a variety of carnivorous plant species.

One of the biggest, and most obvious, is the purple pitcher plant (Sarracenia purpurea).

This dramatic plant has leaves that form sealed 'pitchers', filled with rainwater and digestive enzymes that the plants secrete. Insects are lured to the pitchers with attractive colors and scents, fall in, and become trapped by backward-pointing hairs that make it difficult to climb out.

Small vertebrates such as salamanders may also become trapped. Over time, a rich bacterial community develops within the pitcher, aiding the plant in digestion.

But wait - these are flowering plants. They rely on insects to carry pollen from plant to plant. How do pitcher plants prevent their pollinators from ending up in their pitchers?

They have a few tricks. First, the flowers are borne high on stalks that are often a couple feet tall. This makes the flowers attractive to large, strong flying insects such as bumblebees. The pitchers, meanwhile, are hidden among other plants close to the water's edge, where bumblebees are less likely to forage. The flowers are large, robust, and even have a landing platform for bees to light upon.

Bees are unlikely to slip and fall into a pitcher from these flowers. Even if bees do slip, pitchers tend to be angled away from the central flower. A bee would have to be very unlucky to fall off a flower and land in a pitcher.

Purple pitcher plants are attractive, intriguing, and widespread. Unfortunately, they're also vulnerable. Like most carnivorous plants, they're specialists. They're supremely adapted to their boggy habitats, and don't survive well elsewhere. Loss of habitat due to human development and climate change is a concern. People may also be tempted to dig up these charismatic creatures for their own gardens - an endeavor which is almost certainly doomed to failure. 

If you're interested in these odd and unique plants, they're best enjoyed right where they are - rooted in their boggy shorelines, ordering out for a nitrogen snack or two.

One final intriguing fact that you probably never thought about, although it may make your life richer to know. Just as with animals, pitcher plants can't digest every part of their insect meals. What do animals do with undigested bits of food? Well... you know what bears do in the woods. Do pitcher plants... umm... do this in the bog?

Yes... and no. At the base of each pitcher is a narrow funnel of sorts, where undigested bits of prey accumulate. And stays there. They aren't excreted. An individual pitcher usually lasts for only one growing season, however, before it dies and decomposes. In other words, pitcher plants don't have to worry about constipation.