|General aims and suggestions for classroom use |
The first page of this two-page fact sheet introduces the carnivorous plants of North America and their trap types. This general information is accessible to students across a range of grade levels. The second page focuses on pitfall traps as an example of convergent evolution among plants. Although they look remarkably similar, American pitcher plants are only distantly related to other plants with pitfall traps.
High school students will be familiar with diagrams of evolutionary relationships and cladograms. However, they will benefit if you orient them with the diagram on page two. Most plants are not carnivorous. Because the diagram emphasizes the relationships among carnivorous groups, large groups of noncarnivorous plant families are condensed under one label. For example, the top clade of the diagram includes the primarily carnivorous group of sundews, Venus flytraps, dewy pines, and tropical pitcher plants. Those plants belong to the order Caryophyllales, and the branch labeled "other Caryophyllales" indicates the noncarnivorous members of the order.
One suggestion for using the diagram of plant relationships is to challenge students to interpret the diagram and identify patterns of trap evolution among plants. Ask students to count the separate branches on which they see pitfall traps.
[Answer: Four, tropical pitcher plants (family Nepenthaceae, order Caryophyllales), Australian pitcher plants (genus Cephalotus, order Lamiales), American pitcher plants (family Sarraceniaceae, order Ericales), and two species of bromeliad (monocot plants in the family Bromeliaceae)]
Are the snap traps of Venus flytraps and Waterwheel plants an example of convergent evolution?
[Answer: No, their similar snap traps are due to a common ancestor, one with a snap trap that diverged from its close relatives with sticky traps]
Plant carnivory is an adaptation to life in nutrient-poor environments. Can your students think of plants in other stressful habitats that show convergent evolution?
[Answer: Unrelated plants in deserts share a number of morphological and physiological features; so so those in alpine areas and mangroves]
Returning to carnivorous plant examples throughout the school year will round out your students? views of these flesh-eating plants. Here are a few possible topics.
- Plant structure and physiology - The highly modified leaves are unlike other plant leaves in structure and function, although some traps have photosynthetic abilities. Some species that are aquatic lack roots. The inner walls of most pitcher plants are waxy, making them slippery. When wet from rain or dew, the rim of tropical pitcher plants becomes slippery due to an unusual water-lubricated surface.
- Plant responses to the environment - Snap traps and suction traps are "active" traps in which the plant's trap closes in response to the prey touching trigger hairs, an example of nastic movement.
- Reproduction - Insects play two incompatible roles in the lives of carnivorous plants: they are both prey and pollinators. Most carnivorous plants are perennials that reproduce vegetatively and sexually.
- Interspecies interactions - A variety of insects live unharmed within the digestive pool of pitcher plants. Another case of mutualism involves an ant species that can walk on the slippery surface of Nepenthes plants without falling in. Sympatric carnivorous plants may compete for prey.
- Conservation - Over-collection by plant enthusiasts and habitat destruction are primary threats. CITES regulates the international trade of all carnivorous plants, and the U.S. Endangered Species Act protects two populations of Sarracenia.
Links to more facts and fun
International Carnivorous Plant Society - A wealth of information about the natural history, conservation, and cultivation of carnivorous plants is hosted by this society.
Botanical Society of America - BSA has information and photographs of many carnivorous plants around the world.
Center for Plant Conservation - The CPC provides a profile of Sarracenia oreophila, a carnivorous plant in the CPC National Collection of Endangered Plants.
Tree of Life - The Tree of Life aims to provide evolutionary relationships across all groups of organisms. The link below shows the close relatives of the Sarraceniaceae.
Angiosperm Phylogeny Website - Current views of evolutionary relationships among plants and references are regularly updated on this site.
Albert, V. A., Williams, S. E., and Chase, M. W. 1992. Carnivorous plants: Phylogeny and
- structural evolution. Science 257: 1491-1495.
Bohn, H. F. and Federle, W. 2004. Insect aquaplaning: Nepenthes pitcher plants capture prey
- with peristome, a fully wettable water-lubricated anisotropic surface. Proceedings of
- the National Academy of Sciences 101: 14138-14143.
Cameron, K. M., Wurdack, K. J., and Jobson, R. W. 2002. Molecular evidence for the common
- origin of snap-traps among carnivorous plants. American Journal of Botany 89(9):
Cheers, G. 1992. A Guide to the Carnivorous Plants of the World. Angus & Robertson.
Ellison, A. M. and Gotelli, N. J. 2001. Evolutionary ecology of carnivorous plants. Trends in
- Ecology and Evolution 16: 623-629.
Juniper, B. E., Robins, R. J., and Joel, D. M. 1989. The Carnivorous Plants. Academic Press.
Schnell, D. E. 2002. Carnivorous Plants of the United States and Canada. 2 nd Ed. Timber Press.