Pitcher Pictures

Had my students planting plants today, so:

Pitcher Plant (Sarracenia purpurea), Volo Bog SNA, Lake Co, IL 9/22/2012

Not a very colorful flower, to say the least. It came from one of these oddly-shaped plants:

Pitcher Plant, Volo Bog SNA, Lake Co, IL 9/22/2012

This is a Pitcher Plant (Sarracenia purpurea). Those odd-looking leaves have a rather sinister purpose: they catch, digest, and absorb insects! They attract them with a nectar-like substance, and when the bugs land on the lip of the pitcher, they often slip on the waxy surface. Check out this shot:

Pitcher Plant, Volo Bog SNA, Lake Co, IL 9/22/2012

Do you see those silver hairs? They all point downwards, making climbing back out very difficult. In the bottom of the pitcher, a mixture of water and digestive enzymes slowly breaks down the prey.

I photographed these at Volo Bog in western Lake County, which is the easiest place in the area to see them. They are found in bogs and other nutrient-poor wetlands across the US. Other carnivorous plants (sundews, bladderworts, Venus Flytraps) all tend to live in nutrient-poor soils as well, leading to the hypothesis that carnivory in plants evolved in response to a lack of nutrients, especially nitrogen. The fact that it hasn't evolved elsewhere suggests that there is a cost, and there is. Specialized leaves like these are less effective at photosynthesis. Pitcher Plants actually make regular, photosynthesizing leaves as well, and Ellison and Gotelli showed that adding nitrogen to the soil reduces the number of pitcher leaves produced by the plants. (1)

Oddly, there are Dipteran larvae that actually hatch and develop inside these little pitchers, somehow resisting the digestive enzymes until they can metamorphose into adult flies and mosquitoes (2). They actually eat the other insects that fall in, as well as preying on the protists and rotifers that also inhabit the pitchers. Those protists and rotifers likewise feed on bacteria in the water. This self-contained little ecosystem makes a wonderful test subject, and Cochran-Stafira and von Ende were able to use it to show several trophic cascades based on the presence, especially, of Wyeomyia smithii. (3)

Go back and check out that first shot again -- notice how there aren't any leaves in the picture? Pitcher Plant flowers are borne on long stalks that extend up to a foot above the leaves, like this:

 

Flowering Pitcher Plant, Volo Bog SNA, Lake Co, IL 10/3/2003

The adaptive significance of this should, I think, be fairly obvious. If you're asking insects to carry your pollen to another flower, it would be rude to eat them, so keeping your flowers well away from  your leaves is a good idea!

(1) Ellison, A. M., & Gotelli, N. J. (2002). Nitrogen availability alters the expression of carnivory in the northern pitcher plant, Sarracenia purpurea. Proceedings of the National Academy of Sciences, 99(7), 4409-4412.

(2) Fish, D., & Hall, D. W. (1978). Succession and stratification of aquatic insects inhabiting the leaves of the insectivorous pitcher plant, Sarracenia purpurea. American Midland Naturalist, 172-183.

 

(3) Cochran-Stafira, D. L., & von Ende, C. N. (1998). Integrating bacteria into food webs: studies with Sarracenia purpurea inquilines. Ecology, 79(3), 880-898.