In a world where plants are at the bottom of the food-chain, some individual plant species have evolved ways to reverse the order we expect to find in nature. These insectivorous plants, as they are sometimes called, are the predators , rather than the passive prey. Adaptations such as odiferous lures and trapping mechanisms have made it possible for these photosynthesizers to capture, chemically break-down and digest insect prey (and in some cases even small animals.) There is no reason to fear them though. The majority are herbaceous perennials, usually only 4 to 6 inches high, and nothing like the plant in "Little Shop of Horrors".
Almost all carnivorous plants have a basically similar ecology and several different species are often found growing almost side by side. They are most likely to be found in swamps, bogs, damp heaths and muddy or sandy shores. Drosophyllum lusitanicum from Portugal and Morocco is the one exception, it grows on dry gravelly hills. Like other green plants, carnivorous plants contain the organic pigment chlorophyll. This pigment helps to mediate a chemical process called photosynthesis. This converts light energy into the chemical bond energy of carbohydrate which is utilized as cellular energy, plant growth and development. Water, carbon dioxide, nutrients and minerals are also needed for survival. In wetlands, where stagnate water contains acidic compounds and chemicals from decaying organic matter many plants have a difficult time obtaining necessary nutrients. It is in these nutrient poor conditions that some plants evolved different ways of obtaining nutrients. The ability of carnivorous plants to digest nitrogen -rich animal protein enables these plants to survive in somewhat hostile environments.
The evolution of carnivorous plants is speculative due to the paucity of the fossil record. It is believed that plant carnivory may have evolved millions of years ago from plants whose leaves formed depressions that retained rain water. Small insects would sometimes fall into these water reservoirs and drown, eventually being decomposed by bacteria in the water. The nutrients from the insects would be absorbed by the leaf. The deeper the leaf depression the more insects that could be drowned. This would have created a distinct survival advantage allowing some plants to better compete in nutrient poor soil. As time passed, these plants would evolve more effective trapping mechanisms.
There are more than 500 known species of carnivorous plant, although some are now extinct. Classification is done using the standard binomal system and is based primarily on the floral characteristics of the plants, not the trapping mechanisms. They are divided into two groups based on corolla structure; Choripetalae and Sympetalae. The group of plants categorized as carnivorous belong to seven families, which are recognized by the suffix aceae', and fifteen genera. More than half of the species belong to the family Lentibulariacene that is marked by bilaterally symmetrical flowers with fused petals. The remainder of the species belong to six families marked by radially symmetrical flowers with separate petals. Classification is illustrated in the chart below in addition to the geographic range, the number of species, and the type of trapping mechanism.
Family Genus species Geographic Distribution Type of Trap Byblidaceae
2 Australia Passive flypaper Cephalotaceae Cephalotus
1 S.W. Australia Passive pitfall Dioncophyllaceae
1 West Africa
Passive flypaper Droseraceae
1 Europe, Asia, Africa, Australia Active
1 North & South Carolina
Active steel Family
Genus # of...
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