Carnivorous Plants
Carnivorous plants are any photosynthetic organism that: 1) attracts, 2) traps, 3) kills, 4) digests prey, and 5) absorbs nutrients from animals. They use enzymes, usually a protease, to digest animals. Carnivorous plants have these adaptations for low-nutrient or infertile environment. These plants obtain some nutrients by trapping and digesting various invertebrates, and occasionally even small frogs and mammals. Because insects are one of the most common prey items for most carnivorous plants, they are sometimes called “insectivorous plants”.
Where do they live?
The most common habitat for these plants is in peat bogs, or other similar environments with low nutrient concentrations, but water and sunshine seasonally abundant. Most non-carnivorous plants absorb nitrogen from the soil through their roots, but carnivorous plants absorb nitrogen from their animal prey through their leaves specially modified as traps.
How do they work?
There are several different types of carnivorous plant mechanisms that have evolved (see below). Almost all carnivorous structures are leaf adaptations, although Triantha uses a flypaper method on their flower stalks. They use enzymes, usually a protease, to digest animals to obtain the nitrogen from the animal. In order for a plant to be considered truly carnivorous, researchers must demonstrate that the plant has mechanisms to 1) attract insects, 2) then trap those insects, 3) as well as kill the insects, and most importantly that the plants 4) digest the prey, and then 5) absorbs the nutrients.
Pitfall traps
Leaves folded into deep, slippery pools filled with digestive enzymes
These plants produce volatile organic compounds which lure prey into the traps where they are digested (Dupont et al. 2023)
e.g. Pitfall traps are found in "pitcher plants" from several unrelated families: Sarraceniaceae (Darlingtonia, Heliamphora, Sarracenia), Nepenthaceae (Nepenthes), Cephalotaceae (Cephalotus), and Eriocaulaceae (Paepalanthus)
This feature is an example of convergent evolution among these families
Below: the pitfall traps of the common swamp pitcher-plant (Nepenthes mirabilis), native to southeast Asia
Above: The pitfall traps of the Pitcher Plant (Sarracenia), native to the USA
Below: the pitfall traps of the Albany pitcher plant (Cephalotus), native to Australia
Flypaper traps
Leaves covered in stalked glands that exude sticky mucilage
Insects that are caught in mucilage are slowly dissolved and absorbed
e.g. Sundews (Drosera) and Butterworts (Pinguicula) exhibit flypaper traps
In 2021, a research team published the discovery of sticky hairs on the flower stalk of the western false asphodel, Triantha occidentalis (Lin et al. 2021)
This plant has been demonstrated to be carnivorous, but using the stems that support the flowers (pedicels) instead of using modified leaves.
Below: the flypaper traps of a Butterwort (Pinguicula)
Above: the flypaper traps of a Sundew (Drosera)
Below: flower stalk of Triantha occidentalis showing sticky hairs that catch, dissolve, and absorb small insects
Snap traps
Hinged leaves that snap shut when trigger hairs are touched, trapping prey
Trigger hairs inside the trap are sensitive to touch, and when bent, an action potential propagates to cells in the midrib
These cells respond by pumping out ions, which causes the cells in the midrib to collapse
Changes in the shape of the cells in the midrib allow the lobes, held under tension, to snap shut and capturing the prey
e.g. Venus' flytrap (Dionaea muscipula), and the waterwheel (Aldrovanda vesiculosa)
Given the popularity of the Venus' flytrap, this is not a common method of plant carnivory. There are only two species in the world that use this method,
Above: the Waterwheel (Aldrovanda vesiculosa), an aquatic carnivorous plant
Below: the snap trap of the Waterwheel (Aldrovanda), an aquatic carnivorous plant
Above: the snap trap of the Venus' Flytrap (Dionaea muscipula) with a dead fly
Above: Animated gif showing how the snap traps of a Venus' Flytrap (Dionaea) grow
Above: The snap trap of a Venus' Flytrap (Dionaea) being triggered
Suction traps
Highly modified leaves in the shape of a bladder with a hinged door lined with trigger hairs
These leaves are strange such that they continue to grow during the life of the plant (indeterminate growth) unlike most leaves which have a fixed growth phase (determinate)
This feature is unique to bladderworts (Utricularia), an aquatic and moist-soil plant taxon
Below: the flowers of Bladderwort (Utricularia), in its natural habitat. The leaves with suction traps can be seen just below the water's surface.
Above: Bladderwort (Utricularia)
Below: Animated gif of a suction trap of the Bladderwort (Utricularia), capturing a water flea
Lobster pot traps
Twisted tubular channels lined with hairs and glands that trap prey
These plants tend to catch and digest minute animals, particularly protozoans
e.g. Corkscrew plant (Gensilea) from Africa as well as Central and South America.
Above: the corkscrew plant in it habitat. The lobsterpot traps are below the soil.
Above: the lobster pot traps of the corkscrew plant (Gensilea)
Additional Resources
A Common North American Plant Was Just Discovered to Be Secretly Carnivorous (Science Alert 9Aug2021)
How Plants Evolved into Carnivores (Nature 2017)
Why carnivorous plants eat feces, when they could eat bugs? (Schoner et al. 2016)
Aquatic "Venus Flytrap" faces extinction (Cross et al. 2016)
Is Teasel Carnivorous? (Shaw and Shackleton 2011)
The carnivorous waterwheel (In Defense of Plants 2018)
Fluorescent carnivores (In Defense of Plants, April 2020)