Most plants are content to sit still and take in sunlight and soil nutrients, but when conditions are tough, some plants get hungry! The habit of devouring animal prey has evolved in plants numerous times. In this episode, we discuss the varied strategies and evolutionary history of Carnivorous Plants.
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Plants With Appetites
Most plants get their energy from photosynthesis, and they also need to maintain their bodies with nutrients like nitrogen, phosphorus, and potassium, which they typically get from the soil. But when the local soil is poor in nutrients, some plants turn to another source: animals!
Carnivorous plants include a variety of species that have developed strategies to attract, trap, kill, digest, and absorb nutrients from small animals, usually insects and other invertebrates. Pitfall traps, like those seen in pitcher plants, are leaves folded into slippery pools full of digestive juices; flypaper traps are leaves covered in sticky goo, like those of sundews; snap traps – think Venus flytraps – are hinged leaves that snap shut over prey; the bladder traps of bladderworts suck prey into a digestive bladder; and lobster-pot traps are inescapable corkscrew-shaped channels.
All in all, carnivory is thought to have evolved independently nine times in five different orders of angiosperms, and carnivorous plants are found on every continent except Antarctica.
Not much is known about the evolutionary history of carnivorous plants. Molecular (DNA) studies suggest that carnivory in plants first evolved as far back as the Late Cretaceous, but there’s plenty of uncertainty. The fossil record isn’t much help, either: carnivorous plants tend to be soft-bodied plants (unlike, say, trees) that live in places with low fossilization potential, making them rare in the fossil record. And on top of that, most of the carnivorous attributes of these plants are found on their leaves, which aren’t fossilized often and which aren’t commonly used to identify fossil plants.
Fossil carnivorous plants are almost unheard of. There have been a few suspected carnivorous plant fossils from the Cretaceous Period that have turned out to probably not be carnivorous at all, such as Archaeamphora and Palaeoaldrovonda. More promising are pollen and seeds from relatives of living carnivorous plants from back in the Paleogene. The oldest definitive example of carnivory in plants are some flypaper-trap leaves preserved in Eocene Baltic amber.
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