Lundmosegård Planter.
What are carnivorous plants?
Carnivorous Plants
In this context, we define "meat" as originating from a wide range of animal families, not just mammals. Only a very few plants consume mammalian meat; most instead capture insects, spiders, crustaceans, nematodes, and other small animals.
Therefore, it wouldn’t make sense to label the group as "insect-eating plants" since spiders and many other small animals are not insects. Plants develop the carnivorous syndrome as an adaptation to environments where it is difficult to obtain sufficient nutrients from the soil. This challenge is typically found in acidic and moist to wet habitats where nutrients are unavailable. In Denmark, examples include bogs, wet heathlands, sand in dried-out small lakes, dune hollows, wheel tracks, ditches, and similar areas.
The term "carnivorous plant" is currently used to describe approximately 750–850 plant species across five different plant orders, divided into 19–20 genera. The exact number depends on the species concept used and how carnivorous plants are defined.
The largest genera include Sundews (Drosera) with over 250 species, Bladderworts (Utricularia) with over 240 species, and Pitcher Plants (Nepenthes) with over 170 species. Butterworts (Pinguicula) rank fourth, with approximately 80 species.
In general, most plants can indirectly absorb nutrients from dead animals and insects that decompose on the ground. For example, if a carcass is left to decompose, the surrounding grass grows taller and more vigorous.
Many plants with sticky glandular hairs can trap insects, but they are not considered carnivorous plants. For instance, small animals may be found stuck to plants like potatoes, rhododendrons, and geraniums.
For a plant to be classified as carnivorous, more is required than merely benefiting from a dead animal or trapping small creatures on its leaves.
The common definition of a carnivorous plant includes five simultaneous adaptations that enable the plant to:
- Attract prey,
- Capture it,
- Break it down using enzymes,
- Absorb it,
- And use the nutrients from the prey to promote the plant’s growth.
In recent years, researchers have discovered that some species rely on various predatory insects to help break down the prey they capture. These predators consume the animals attracted and trapped by the plant, and their excretions are absorbed through openings in the plant’s leaves. These predatory insects avoid being caught by the plant, creating a mutualistic relationship in which the plant provides shelter and a food source, while the insects assist with external digestion.
The best-known example of this mutualism involves the two carnivorous shrubs in the South African genus Roridula. However, more such relationships are being discovered, blurring the lines of what constitutes a carnivorous plant. Roridula cannot produce its own enzymes, relying on predatory bugs for the third criterion in the definition of carnivorous plants.
Other examples of predatory insects are found in some sundew species, which can produce enzymes themselves. The details of these partnerships are not yet fully understood.
A few Nepenthes species have abandoned the capture of insects and other small animals and instead catch larger prey, such as small rodents. Others have developed relationships with bat species, which spend their days inside the plant’s specialized traps and pay "rent" with nutrient-rich excrement that the plants absorb.
Butterworts can absorb nutrients from pollen that lands on their leaves and are considered herbivorous.
The anatomical adaptations that transform leaves into trapping mechanisms are divided into five groups:
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Pitfall Traps
Animals, attracted by sugary substances, fall into a cavity filled with enzyme- and/or bacteria-enriched fluid, where they dissolve—if space allows. Once the traps are full, digestion must await the breakdown of previous prey. Escape is impossible. These traps are found in genera such as Darlingtonia, Sarracenia, Heliamphora, Cephalotus, Nepenthes, Catopsis, and Brocchinia. -
Snap Traps
This remarkable adaptation allows plants to execute a rapid movement triggered by contact with one or two hairs within a 20-second interval. The prey is trapped between two tissue surfaces functioning as a stomach. Known examples are in the genera Dionaea and Aldrovanda. -
Suction Traps
These typically function in water, where a vacuum inside the trap is triggered by contact, sucking in the prey for digestion. This type of trap is found in bladderworts of the genus Utricularia. -
Lobster Pot Traps
Specialized underground leaves guide soil-dwelling prey into tubes, where they encounter a "stomach" with no escape route. This adaptation is found in the genus Genlisea, a lesser-known relative of bladderworts and butterworts. -
Flypaper Traps
Prey lands, becomes stuck, struggles, and is enveloped in enzymes that penetrate its airways. The prey dissolves from the inside, its inner contents spilling out onto the plant’s leaves, where they are absorbed through specialized openings. This group includes genera such as Drosera, as well as Drosophyllum, Byblis, Pinguicula, Roridula, Triantha, and Triphyophyllum.
