Insect Eaters: 10 Carnivorous Plants
Recently I wrote a hub examining the diversity of pitcher plants in Pitcher Plant Diversity: A Look At 10 Species. In this hub I'll take a look at 10 more carnivorous plants (that aren't pitcher plants) including some well known species such as the Venus Fly Trap and Sundews as well as many lesser known, but equally strange species. These plants have remarkable adaptations to help them capture prey, the nutrients from which they require to grow in often low-nutrient soils. Lets begin by starting with a plant that everyone will recognise, the Venus Flytrap, shall we?
Looking like some alien triffid jaw from a distant planet, it is not hard to see where the common name of Dionaea muscipula, the Venus Flytrap originates from. These iconic traps snap shut when insects or spiders crawl across and trigger the fine hairs in the center of the trap. The traps have the remarkable ability not to trigger unless a different hair is triggered within 20 seconds, or the same hair is triggered a second time in rapid succession. This is an adaption to stop the trap from wasting energy when triggered by a falling leaf or other debris. Once the prey is caught inside, the trap releases digestive enzymes that dissolve it, allowing the trap to absorb the nutrients contained within the prey item. If the insect tries to struggle it will repeatedly trigger the hairs, causing the trap to tighten further. The teeth (cilia) mesh together in such a way that there are still small gaps present when fully shut. This is thought to allow small insects to escape as the benefit of capturing them would be less than the costs involved with digesting them. The traps take about 12 hours to re-open.
Native to parts of Asia, Africa, Australia and Europe, Aldrovanda vesiculosa has a wide and patchy distribution. It is an aquatic plant that feeds on aquatic invertebrates using a trap very similar to that of the venus flytrap. The traps are arranged in whorls around a central stem, which is the reason behind its common name, the Waterwheel Plant. The tiny, 3mm long traps have air pockets in their stems that allow the traps to float clear of the rest of the plant. Much like the venus flytrap, the traps of the Waterwheel Plant have trigger hairs that cause the trap to suddenly snap shut when triggered by a passing aquatic invertebrate. The traps only take at most 20 milliseconds to close, making it one of the fastest examples of plant movement in the world.
Drosera rotundifolia is one of the most widespread Drosera species. It is found across much of northern Europe, Siberia, northern North Amercia, Korea, Japan and even New Guinea. Fittingly it is known by the common name of Common Sundew as well as Round-Leaved Sundew in reference to its round leaves. The leaves form a small rosette only about 5 cm (2 inches) wide. At the end of each leaf is a paddle-shaped tip which is covered in red, sticky mucus-producing filaments. These sticky filaments are used to catch their prey, a mechanism known as a flypaper trap. The mucus contains sugars which attract insects, as does the bright red colour of the filaments and sunlight reflecting of the mucus. If the insect lands on or comes in contact with the filaments they become stuck. Struggling is more often than not useless as they end up just getting caught on more of the sticky filaments, strengthening the grip of the plant. Eventually the insect will die of exhaustion and digestive enzymes will be released to dissolve the insect after which the contained nutrients can be absorbed by the leaf. All sundews also exhibit a tactic known as thigmotropism, where the leaf can move (curl inwards) in response to prey movement, increasing the number of filaments that make contact with the prey item. Sundews prefer growing in damp wetland conditions.
Native to parts of Portugal, Morroco and Spain, Drosophyllum lusitanicum is distinct in that it is one of the few carnivorous plants able to grow in dry, alkaline soils. It goes by the common names of Dewy Pine or Portuguese Sundew. The leaves have sticky, mucus-covered filaments and catch prey in a similar manner to Drosera rotundifolia above, although this plant doesn't respond to movement like Drosera rotundifolia does. This plant has a sweet aroma which it uses to attract its insect prey. Prey making contact with the sticky mucus will become traped. They will struggle to escape but will only entangle themselves further. Digestive enzymes are then released, dissolving the insect and allowing the nutrients contained to be absorbed by the plant.
Native to the southeastern coastal plains of the United States of America, Utricularia inflata is a large, submerged, aquatic, carnivorous plant. It is known by several common names including the Swollen Bladderwort, Inflated Bladderwort and Large Floating Bladderwort. This bladderwort has no true leaves or roots and is instead made up of filiform stolons (runners with thread-like projections). Occasionally the stolons will produce tuber-like structures in the sediment of the body of water that they are growing in. They also occasionally produce what is termed a float, which is a whorl of spongy projections that can float on the surface of the water and act as a platform for flowering to occur from. The bladder traps themselves from which the plant gets it common names occur underwater along the stolons. They are round hollow sacs that after forming are pumped empty of water by the plant, this pumping causes a partial vacuum to occur. There is a trapdoor on each bladder that has a branched trigger hair. These hairs act as leavers that when bumped by small aquatic invertebrate will open the trapdoor slightly, breaking the partial vacuum. This causes water to flow into the bladder, sucking in with it whatever happened to bump the trigger. The trapdoor then snaps shut, enclosing the prey inside where digestive secretions start to dissolve it.
Pinguicula moranensis is a small, attractive flowered succulent that has two forms, almost like a plant version of Dr. Jekyll and Mr. Hyde. During Winter it grows as a relatively benign ring of non-carnivorous succulent leaves. During Summer when it is wetter and there are more insects flying around it turns into a monster. It produces a rosette of leaves that are covered in sticky, mucus producing hairs that trap insects looking to drink from them. The leaves have the ability to move slightly as the insect struggles (called thigmotropism) causing even more of the sticky hairs to come in contact with the insect, sealing its fate. In its Summer form the plant produces digestive enzymes when they capture prey, the dissolved nutrients are then absorbed through pores in the wax coating (cuticle) over the skin of the leaf. The plant however can also lose water across these pores. Winter is the dry season in Mexico and Guatemala where this plant originates from and in its Winter form it does not have these pores, preventing dehydration that would occur otherwise.
Plants in the genus Genlisea are collectively known as Corkscrew Plants and are named for their unique underground traps. Corkscrew plants have no actual roots. The plant has regular photosynthetic leaves that form a rosette above ground but what appears to be roots in the photograph to the right are actually modified underground leaves. They can absorb water and provide anchorage jut like normal roots, but they are also carnivorous. Corkscrew plants specialise in capturing underground invertebrate prey. The underground leaves spiral around and have unidirectional hairs that lead their prey to a fork where the entrance to the trap chamber is. The walls of the chamber are also lined with hairs that allow the prey to enter, but hinder escape. Inside they are dissolved by digestive enzymes and absorbed by the plant.
Byblis liniflora is native to parts of Australia, New Guinea and Indonesia. Plants in the in genus Byblis are commonly known as Rainbow Plants because of the way the mucus covered, sticky hairs on their leaves refract bright light into a rainbow, however this effect isn't unique to this genus and can also be observed in the genera Drosera, Drosophyllum and Pinguicula. Prey that land on the sticky hairs become trapped, eventually dying of exhaustion or suffocation if the mucus blocks their breathing spiracles. This plant produces at least one digestive enzyme to digest captured insects but also has an interesting relationship with a genus of true bugs (Setocoris species). These bugs can walk across the sticky hairs without being captured themselves. The bugs are insectivorous and feed on the prey the plant has captured. While this may seem like a one-sided relationship, the plant benefits when the bug defeacates around the plant, providing nutrients that the plant might otherwise have difficulty digesting and absorbing.
Triphyophyllum peltatum is a carnivorous plant native to tropical rainforests of western Africa. It is interesting in that it has a 3-stage lifecycle, only one stage of which is spent as a carnivorous plant. It is the only species within the genus Triphyophyllum. In its first stage it has simple lance-shaped leaves with no distinguishing characteristics. Once it grows a bit more it starts to develop long leaves dotted with sticky muscus producing glands that capture insects, similar to Drosophyllum lusitanicum above. After acquiring nutrients from insects in this stage it then enters the adult stage of its lifecycle where it grows as a long, twinning liana (a woody climbing vine) and has non-carnivorous leaves.
Native to southern Venezuela, Brazil and Guyana, Brocchinia reducta is one of the few true carnivorous bromeliads. Most bromeliads after rain hold a reservoir of water in the center of their overlapping leaves. This bromeliad goes a step further and releases digestive enzymes into and has symbiotic bacteria within the reservoir. These help to digest and dissolve any insects that fall in, after which the leaves can absorb the nutrients released. To attract its prey the liquid in the reservoir has a sweet scent. The plant also has scales which are highly reflective to UV light. Insects are attracted to UV light reflected off surfaces (many flower also have UV reflective patches for this purpose) and will land on these scales. The scales however are loose and provide a poor footing, causing the insect to fall into the water reservoir below and drown.