The Carnivorous Plant FAQ v. 12

Q: Are there any vegetarian carnivorous plants?

N. ampullaria
N. ampullaria
A: Now, you must admit, this is a weird question.

Believe it or not, I have been asked this question a number of times, and have always told people that, no, there are no vegetarian carnivorous plants. But then I started thinking more about it, and I think that there are in fact vegetarian carnivorous plants! Hell, these plants are even vegan, as you will see.

The first plant I am thinking about is Nepenthes ampullaria. This plant is, no doubt, a carnivorous plant; its pitchers are quite effective at capturing and digesting bugs. However, it does something that no other Nepenthes species does. It blankets the rainforest floor with clusters of "ground pitchers" that are really cute. They look like clumps of mushrooms.

It has been suggested that this plant may use these ground pitchers to capture vegetative detritus that rains down from the overhanging rainforest canopy. A great deal of material falls from above in the rainforest, and this pitcher plant may use its pitchers to capture the decaying material and hoard it for itself, before any competing plants can get it at. So this plant may be at least supplementing its carnivorous diet with a vegetarian side dish.

By the way, Nepenthes ampullaria rarely makes "upper" pitchers. So perhaps it is evolving away from a mixed diet. Perhaps in a few million years there will be an entirely vegetarian Nepenthes? Probably not---we will have made the planet unlivable long before then.

U. purpurea
U. purpurea

Pinguicula macroceras
Pinguicula macroceras

The second example of a vegetarian carnivorous plant might be some species of Utricularia. For example, Utricularia purpurea may no longer be carnivorous. It might be that the bladders that operate as carnivorous stomachs for (presumably) all the other bladderworts have been railroaded into a different function for Utricularia purpurea. It has been suggested that the bladders now function to create a safe little home for algae and other organisms to live. The Utricularia extracts nutrients from these singe-celled plants in a sustainable way (much like humans might harvest asparagus shoots from a bed of plants, keeping the plants alive for the long term). Is this a vegetarian plant? Could be! On the other hand, it hasn't quite lost all its carnivorous attributes, for Mary Treat observed that prey captured by the sucking traps were dissolved by enzymes (so Lloyd tells us).

Taking things even further, it has been observed that some species of Utricularia actually kill and digest algae, making them real killing vegetarians (Mette et al. 2000; Peroutka et al. 2008; Seine et al. 2002). Barthlott et al. (2007) note that more than 80% of the prey spectrum in U. australis consisted of algae. How these algae get into the bladders is as yet unclear.

My favorite example, though, is for a wide variety of plants in the genus Pinguicula. Because of their architecture--with a flat rosette of open leaves--these plants capture a lot of pollen on their leaves. This pollen is digested by the plant. Since, in this case, the pollen consists of living plant cells in a self-contained structure, I can to my own satisfaction argue that Pinguicula rosettes capture live plants, kill them, and consume them. Indeed, in one study more than 50% of the proteins in P. vulgaris were attributed to captured pollen grains (although I admit to having this information secondhand, from Barthlott et al. 2007).

So now, I must ask about the very nature of vegetarianism in carnivorous plants. Would such plants be viewed, by other plants, with the same derision that human vegetarians often view omnivorous Homo sapiens? Would a plant be considered more ethical, or moral, by other plants if it chose to only eat animals instead of plants? I wonder.

Page citations: Barthlott, W. et al. 2007; Clarke, C. 2001; Legendre, L. 2000; Lloyd, F.E. 1942; Peroutka, M. et al. 2008; Richards, J.H. 2001; Seine, R. et al. 2002.

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Revised: 2018
©Barry Rice, 2018