Pitfall, pitcher, urn, snap, bladder, sticky - all of these words have been used to describe the means by which carnivorous plants acquire their prey. But what about "lobster pot?" Believe it or not, there is a genus of plants that has evolved a strategy for catching prey that would make lobster fishers proud.
The genus in question here is Genlisea. It comprises roughly 30 species of what are common called "corkscrew plants" native to both Central and South America as well as Africa. The carnivorous habit of this group would not be readily discernible to the casual observer. These plants are small and can be found growing in saturated, nutrient-poor soils.
Above ground they resemble their cousins the bladderworts (genus Utricularia). The flowers are quite showy and most species present them in either yellow or purple. At ground level sits a dense rosette of leaves. These are only part of the foliar picture. The corkscrew plants produce an entirely different set of leaves that take care of their nutrient needs. To find these, however, one must look underground.
Genlisea have no roots. Instead, they are anchored in the ground by truly bizarre, highly modified leaves. They produce no chlorophyl and look absolutely nothing like what we expect leaves to look like. Instead, they form a hollow cylinder that corkscrews down into the permanently saturated soil. This is where its carnivorous habits take place.
Along the length of each corkscrewed leaf runs a slit-like opening. Along the mouth and all inside the chamber are backwards pointing hairs. Like a lobster pot trap, animals can enter these slits with ease. Getting back out, however, is nearly impossible. The only option the trapped critters have is to continue on to their doom. Towards the end of the traps sits a chamber where most of the digestion takes place. A quick caveat here: to say animals is a bit misleading. Most of what these plants are feeding on are small, soil-dwelling protozoans.
Regardless, the traps are quite efficient. It was only recently realized that this was a true form of carnivory. Darwin himself had suggested it after careful examination but it wasn't until the 1990's that any digestive enzymes were detected. Still, it is a bit of a mystery exactly if or how these plants attract prey. Some researchers have found substances within the cylinders that are hypothesized to act as chemical attractants. More work needs to be done on this.
The traps don't spell certain death for all life. In an interesting study, researchers identified 29 different kinds of algae living inside the traps. Since dissolved oxygen is quite low inside, most of these algae are specialized for anoxic environments. The relationship between the algae and the plant is not certain at this point. Some think it is commensal whereas others feel that the algae may compete with the plant for phosphorus. Again, more work is needed.
The carnivorous nature of this genus isn't the only interesting aspect of their evolutionary history. Some member of this genus, specifically Genlisea aurea, have some of the smallest genomes of any flowering plant. This is not an ancestral state for this group meaning that at one time, the common ancestors had larger genomes but subsequent pruning has gotten rid of most of the "non-coding" sequences. Though there is plenty of speculation as to why this has happened, it is still anyone's guess at this point.