Carnivorous plants have left very few fossil records. For example, of the Aldrovanda vesiculosa, archeologists have found only one leaf and a few seeds, according to the International Carnivorous Plant Society. The lacking fossil records inhibit efforts to track the evolution of carnivorous plants. As a result, carnivorous plant evolution must mostly be determined by observing current species.
Carnivorous plants must be between 60 and 125 million years old, because they are all flowering plants and flowering plants have only been around for this length of time, according to the International Carnivorous Plant Society. They also must have evolved after insects evolved, since they primarily feed off insects.
Carnivorous plants get their main food through photosynthesis. Since they grow in regions that are nutrient-poor, they likely became carnivorous in response to a lack of nutrients in their soil regions. They capture flies and dissolve them using an acid that is a specialized protein similar to pepsin, according to Harvard University. The plant directly absorbs the nutrients that are broken down in the fly. Thanks to these nutrients, carnivorous plants grow rapidly and develop several more traps to capture insects.
Charles Darwin stated that organisms that hold similar traits are likely to have similar ancestors. Based on fossil records, carnivorous plants and angiosperms are polyphyletic, meaning that they have a common ancestor, but are different enough to be a separate family, according to Harvard University. Carnivorous plants are members of the sundew family and many researchers theorize that they evolved around the same time that other plants evolved to develop flowers. Researchers now consider carnivorous plants to be a part of four different flowering plant lineages and four different orders. In total, six different plant species have evolved to actively capture insects.
The closing traps of the carnivorous plants--such as those of the Venus flytrap--evolved to direct energy to certain areas of the plant more quickly than most plants do. The plants' traps must close fast enough to catch the flies within, or else they waste valuable energy closing. These plants must also develop enough energy to be able to construct their highly complex closing leaves.
Carnivorous plants have evolved several different trapping mechanisms. In the "pitfall" technique, the plant sucks the insect into a rolling leaf, engulfing it. "Flycatchers" trap insects with glue. "Snap" traps are specialized leaves that close and trap insects. "Bladder" traps suck insects in, as water flows into the plant. "Lobster-pot" traps have easy entrances and difficult exits, trapping insects within. Although these capturing methods differ, all carnivorous plants benefit from dissolved insects to release their contained nutrients.