Carnivorous Plants 101

The exact number of carnivorous plant species is a matter of some debate. The precise count varies depending on different factors, such as whether to include subspecies and plants that have gone extinct, as well as whether to count plants that are labeled as “potentially carnivorous” (meaning that they might be carnivorous but science has not yet proven it).

That being said, most people agree that there are somewhere between 600 and 1000 species, with 8 Families that are comprised exclusively of carnivorous plants.

These Families are: Droseraceae, Drosophyllaceae, Byblidaceae, Nepenthaceae, Cephalotaceae, Sarraceniaceae, Lentibulariaceae, and Roridulaceae. (I’ll be discussing these specific Families later on in individual posts, so stay tuned for that!)

In the picture at the end of this post, you can see a phylogenetic tree (originally published in the Journal of Experimental Botany) which shows the 8 exclusively carnivorous plant Families as well as their close relations (including some Families that have only one or two carnivorous species, such as the Bromeliaceae family).

[Exclusively carnivorous Families are highlighted in green.]

According to one of my primary research resources when it comes to carnivorous plants, it is possible to differentiate three digestive mechanisms when it comes to the digestion process of carnivorous plants.

These three digestive mechanisms are as follows:

Continuous Digestion In A Chamber: Found in carnivorous plants with pitfall traps, this digestive mechanism involves a trap that forms a closed digestive chamber that is continuously filled with fluid.

Cyclical digestion in a chamber: This digestive mechanism involves a trap that forms a closed digestive chamber only when the trap catches prey; this means that digestive fluid can only be found in the trap when it is closed. You can see this sort of digestive mechanism in Dionaea and Aldrovanda plants.

Carnivorous plants can be grouped into three types: active, semi-active, and passive. These categories relate to the traps that the plants use to ensnare their prey, specifically the level of activity and/or motion that is present.

ACTIVE: These plants catch insects with traps that either snap closed on potential prey or suck them in when they sense them in close proximity.

SEMI-ACTIVE: Sometimes also called the ‘adhesive’ type, these plants have special glands that exude sticky substances that create a flypaper-like texture on their leaves. Once the prey is stuck, the leaf may roll closed to cover the trapped insects.

PASSIVE: Unlike plants with active and semi-active traps, carnivorous plants with passive traps display no overt motion when it comes to trapping their prey. Instead, they rely entirely on bright patterns or sweet-smelling nectar (or a combination of the two) to lure in insects (or in the case of incredibly large pitcher plants, even small rodents) which then become trapped and unable to escape.

Also known as South American pitcher plants, the twelve species that make up the Heliamphora genus have an extremely limited distribution range: they can be found on “the sandstone formations of the South American Guiana plateau in the border region between Venezuela, Brazil, and Guiana”. Heliamphora plants are notable for the way they “colonize infertile soils on sites that are kept constantly moist by fog, with high levels of sunlight.”

First discovered in 1838 by German naturalist Robert Hermann Schomburgk (who encountered the species now known as Heliamphora nutans), these plants have well-developed root systems and feature funnel-shaped pitchers that function as pitfall traps to capture insects. Unlike other types of pitcher plants, however, Heliamphora plants do not have any digestive enzymes of their own, and instead rely on the bacteria living in within the fluid of their pitchers to help break down captured prey.

Hello, everyone! I've noticed some curiosity (and received some questions) about Genlisea plants, specifically about how they ‘eat’ and take in nutrients without roots. This led me to realize that this is a perfect opportunity for me to ramble on (in an educational manner) about rhizophylls! So here we go!

Also sometimes known as “snare leaves”, rhizophylls are a plant organ that greatly resemble roots while not actually being roots. These snare leaves are in fact the traps that Genlisea plants use to capture and digest their prey (hence the term ‘snare’.).

Genlisea plants get their common name of corkscrew plants from the unique pronged appearance of these snare leaves; originally Genlisea plants were known as “Forked Trap” plants because of this shape, until Peter D’Amato first began calling them corkscrew plants in the first edition of his carnivorous plant book, The Savage Garden (which I highly recommend, by the way; I own a copy and it is fabulous).

Generally speaking, rhizophylls range in size from two inches to six inches in length.

To quote The Savage Garden (which describes the anatomy of a rhizophyll far better than I ever could, although I may attempt to put it into my own words someday) “a cylindrical stalk extends downward from the base of the plant…midway down, this swells into a hollow bulb-like chamber (the ‘stomach’ of the trap). [The stalk] then continues downward as a tube-like structure, then abruptly branches into tow corkscrew-like appendages. At the base of the fork where it branches in a slit-like mouth, which spirals all the way down both prongs of the trap”.

But what, you may ask, do these specially designed traps actually capture? The answer to this question is: very tiny things! Specifically, protozoans and other very small lifeforms. “Minute microfauna,” is the technical term, I believe.  

No one is quite sure how Genlisea plants actually lure in these tiny organisms. It’s possible, I suppose, that these tiny little organisms just swim into the traps unaware of their impending doom, but there’s also been some debate about whether or not there’s something inherent to rhizophylls that attracts prey, or if there’s some sort of special suction/vacuum effect that pulls nearby prey in (similar to waterwheel plants).

In any case, once the prey is inside the rhizophylls, there are tiny upward pointing hairs that 1) prevent them from escaping and 2) force them to keep moving up the tube…all the way to that bulb-like chamber that functions as the digestive ‘stomach’ of the plant (where the digestive juices then break down the prey for nutrients).

Anyway! Rhizophylls, in my honest opinion, are a very cool plant organ, and are an extremely clever and unique carnivorous adaptation. Sadly, since most people grow Genlisea in soil rather than in water, you don’t really get to see the snare leaves themselves very often (they are after all, subterranean). That being said, sometimes someone will do something incredibly clever like Geoff Wong did; he once grew a Genlisea in a way that allowed the snare leaves to be visible in an aquarium-esque setup below the actual plant itself (he incidentally also won Best of Show in San Francisco with that Genlisea plant, and a picture of that plant [like the one you see above] is one you’ll often see in relation to corkscrew plants because it really emphasizes how incredible the rhizophylls are).

In any case, that concludes my ramble on rhizophylls! Thank you all for tuning in! As always, if anyone has any further questions or comments, feel free to hit up my ask box! I’m always happy to chat about carnivorous plants, so drop in anytime! <3

Nepenthes spectabilis

Nepenthes villosa is one of the more difficult but rewarding species, just don’t make a mistake! Expertly grown by @nepenthesgod .