Bog Monsters

As a layman of botany the idea of carnivorous plants has perplexed me. The capturing and eating of other creatures seems like it ought to be limited to animals, since animals are mobile and plants are not. Almost all plants survive and thrive in the world through photosynthesis. They do not need to feed on animals to survive. But, what about the group of plants that are carnivorous? As stationary plants, why and how do they eat critters?

This topic was stimulated by my assignment today at the Conservatory Greenhouse of the University of Minnesota. My task was to clean several large tanks of water filled with aquatic plants. While cleaning the tanks I realized many of the plants were classified as carnivorous. What is it about the aquatic environment that causes plants to eat - in effect - other creatures?

The short answer is carnivorous plants evolved in nutrient-poor settings such as pond water which is naturally low in the amount of nitrogen needed to synthesize proteins. To compensate for the lack of proteins the carnivorous plants capture and digest the proteins they need from the unfortunate insects that happen to step on them. Like other non-carnivorous plants they gain most of their energy from photosynthesis, but the nitrogen they need for making protein is supplemented by digesting critters.

Here are a few examples of the plants I was handling today:

Venus fly trap (Dionaea muscipula)

This species of flytrap is endemic to the Carolina coast of North America. The species is threatened by habitat loss - since 1980 the number of plants has declined by over 90% in the Carolinas as agriculture and housing developments expand. But as a popular house plant it has been saved from extinction. Most of the flytrap's victims come in the form of crawling insects and spiders. Despite its name, flying insects account for less than 5% of its meals (Wikipedia). The modified leaves take less than a tenth of a second to close, forming a mini-stomach with digestive enzymes, the prey are consumed in about a week's time. The leaves will then open again, ready for use.

Drosera regia (king sundew)

This species of sundew is native to South Africa. They are closely related to venus flytraps. Genetic studies suggest the flytraps evolved from ancestors of sundew plants. Sundews have been referred to as flypaper traps for their ability to express sticky mucus from hair-like glands which cover the leaves. The sticky hairs capture flying insects that land on the leaves. The photo above shows several small flying insects stuck to the leaves of the plant. Nutrients from the captive insects are absorbed by the mucus glands and leaf surfaces. The leaves have the ability to curl up around the prey like an octopus tentacle.

Pitcher plant (Sarracenia purpurea)

There are many species of pitcher plants around the world. Some plants produce pitchers large enough to trap small rodents and salamanders who happen to slip into the cups. But, the species in the picture (above) is a smaller species, native to the Great Lakes region - including Minnesota - and the eastern seaboard of North America. The pitchers are approxmately 6 inches in length and 2 inches in diameter. As with other pitcher plants, this species fills with rain water where hapless insects go to drown. Unlike many other pitcher plants, this species does not have digestive enzymes. Rather, the water contains bacteria, mosquito larva, and protists which digest the critters for the plant to absorb. I've personally observed this plant growing out of doors in a bog at the Minnesota Landscape Arboretum.

Although it was great fun to explore the variety of plants sitting in the water tanks, the majority of my shift was used to empty, clean, and refill the tanks with nutrient-poor water that had been purified by reverse osmosis - so called RO water.

Newly cleaned tank, with a group of drosera plants in the gray tub.

Newly cleaned tank of aquatic plants, some floating without the need for a pot.