Plants and animals have evolved to fill all available habitats and ecological niches. Plants inhabit every possible environment including water, air, soil (wet and/or dry), other plants and also animals.
Green plants contain the organic pigment chlorophyll. When provided with light, carbon dioxide, water, and essential minerals they produce carbohydrates through a chemical process called photosynthesis mediated by the pigment chlorophyll. The light energy is converted into the chemical bond energy of a food molecule. The carbohydrate food molecules are utilized by the plant for cellular energy and as the basis for producing other molecules which are essential for the plant's growth and development. Usually the minerals and water are taken up by the root system and conveyed throughout the plant, including the sites of photosynthetic activity.
Plants have evolved to utilize all available habitats such as arid and semi-arid regions, moist and waterlogged areas, full sunlight to complete shade, from tropical to Arctic climates. Thus, it would be logical to expect that plants would evolve to survive in nutrient-poor soils and/or water.
The evolution of carnivorous plants is speculative due to the paucity of the fossil record. Flowering plants (angiosperms) began to evolve during the Cretaceous period of the Mesozoic Era. The flowering carnivorous plants, the topic of this book, therefore, cannot be older than 136 million years. The oldest carnivorous plant fossil is Aldrovanda pollen found in rock of the Eocene period that began 53 million years ago and ended 37 million years ago. The earliest Droseraceae pollen is found in the Miocene period, 26 to 12 million years ago.
Many plants today are adapted to foliar feeding. That is, when a nutrient (fertilizer) solution is sprayed on the leaves, the plant can absorb the nutrients through the leaves into the plant body. The beginning of carnivory could have taken place when some leaves formed shallow depressions in which rain water was retained for a period of time after a rain shower. These leaves would be ideal water reservoirs for insects. In the process of obtaining a drink, some insects would drown and eventually be decomposed by bacteria living in the water. The nutrients released into the water could have been absorbed by the leaf into the plant body. This process, similar to foliar feeding, would provide a distinct advantage to plants growing in nutrient-poor soils barely able to provide sufficient nutrients for growth. It would have provided them with a distinct survival advantage. The deeper the depression in the leaf, the more insects could be drowned and decomposed. In times of stress or overcrowding the plants that could derive nutrients through their leaves would be better able to compete in nutrient-poor soil. The plants able to obtain additional nutrients from their leaves would be stronger and healthier and more likely to produce offspring. As time passed, those plants that evolved more effective traps, means of attracting insects and directional guides—that is, the arrangement of nectar-producing glands and hairs that lead the prey into the trap— would be better able to survive in nutrient-poor soils.
The characteristics that distinguish carnivorous plants—such as visual and odiferous lures, directional guides, secreting glands, absorbing glands, trapping, and rapid movement — are found in various plants not considered carnivorous. Some non-carnivorous plants trap insects to effect pollination. Plants such as Mimosa pudica and the Telegraph plants (Desmodium) have leaves that exhibit rapid motion. Some tree leaves secrete a sticky substance that falls to the ground. While all of the individual characteristics of carnivorous plants can be found in other plants, when they are all combined in the same plant the organism is truly unique, a carnivorous plant whose modified leaves can trap and digest prey lured to the plant. The digested materials are utilized by the plant for its growth and development. The fascination with carnivorous plants partly stems from the ability of these plants to reverse the order we expect to find in nature. Carnivorous plants are the predators rather than the passive prey.
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