There are over a quarter of a million species of flowering plants. Of these, only around 630 are known to be carnivorous. Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods. Carnivorous plants appear adapted to grow in places where the soil is thin or poor in nutrients, especially nitrogen, such as acidic bogs and rock outcroppings.
True carnivore has probably evolved independently at least six times; however, some of these “independent” groups probably descended from a recent common ancestor with a predisposition to carnivorous.
Some groups seem particularly fertile ground for carnivorous pre-adaptation, although in the former case, this may be more to do with the ecology of the group than its morphology, as most of the members of this group grow in low-nutrient habitats such as heath and bog.
Let’s get a look at some of the most dazzling but poisonous ‘meat-eater’ plant species.
1. Venus Flytrap
The Venus Flytrap, Dionaea muscipula, is a carnivorous plant that catches and digests animal prey—mostly insects and arachnids. Its trapping structure is formed by the terminal portion of each of the plant’s leaves and is triggered by tiny hairs on their inner surfaces.
When an insect or spider crawling along the leaves contacts a hair, the trap closes if a different hair is contacted within twenty seconds of the first strike. The requirement of redundant triggering in this mechanism serves as a safeguard against a waste of energy in trapping objects with no nutritional value.
Dionaea is a monotypic genus closely related to the waterwheel plant and sundews, all of which belong to the family Droseraceae.
The Venus Flytrap is a small plant whose structure can be described as a rosette of four to seven leaves, which arise from a short subterranean stem that is actually a bulb-like object. Each stem reaches a maximum size of about three to ten centimeters, depending on the time of year;longer leaves with robust traps are usually formed after flowering.
Flytraps that have more than 7 leaves are colonies formed by rosettes that have divided beneath the ground.The trapping mechanism is so specialized that it can distinguish between living prey and non-prey stimuli such as falling raindrops; two trigger hairs must be touched in succession within 20 seconds of each other or one hair touched twice in rapid succession, whereupon the lobes of the trap will snap shut in about 0.1 seconds.
Drosera, commonly known as the sundews, comprises one of the largest genera of carnivorous plants, with at least 194 species. These members of the family Droseraceae lure, capture, and digest insects using stalked mucilaginous glands covering their leaf surface. The insects are used to supplement the poor mineral nutrition of the soil in which they grow. Various species, which vary greatly in size and form, can be found growing natively on every continent except Antarctica.
Aldrovanda is a free-floating and rootless aquatic plant. This plant is closely related to the Venus flytrap Dionaea muscipula, and shares many of its attributes–it functions as a snap-trap carnivore, just under water! A common name for it is the waterwheel plant because a single whorl of leaves, cut from a stem, is wheel-like, as you can see to the right! The genus name commemorates the Italian naturalist Ulisse Aldrovandi (1522-1605). In fact, the name for the genus was originally “Aldrovandia”, but Linnaeus misspelled this, and we use the incorrect spelling even today.
Each leaf in a whorl terminates in a little clam-like trap. Exactly how the trap captures prey is a little complicated. Just like the traps of a Venus flytrap, the trap lobes of Aldrovanda contain trigger hairs. When stimulated, these cause the traps to close. SNAP! The closure takes about 1/4 to 1/2 second, which is impressive when you reflect upon the fact that the trap lobes must push water as they close. If no prey is captured, the trap reopens in ten to twenty hours.
The strange snapping behavior of the plant was observed by De Sassus as early as 1861, but it was not until Darwin’s careful work was there proof it was probably carnivorous. We now know that indeed, the traps produce phosphate-digesting enzymes, and that traps fed with radioisotope-labeled Daphnia absorb the prey.
Pinguicula, commonly known as the butterworts, is a genus of carnivorous plants that use sticky, glandular leaves to lure, trap, and digest insects in order to supplement the poor mineral nutrition they obtain from the environments. Of the roughly 80 currently known species, 12 are native to Europe, 9 to North America, and some in northern Asia.
The largest number of species is in South and Central America. Butterworts can be divided roughly into two main groups based on the climate in which they grow; each group is the further subdivided based on morphological characteristics. Although these groups are not cladistically supported by genetic studies, these groupings are nonetheless convenient for horticultural purposes.
Tropical butterworts either from somewhat compact winter rosettes composed of fleshy leaves or retain carnivorous leaves year-round. Temperate species often form tight buds composed of scale-like leaves during a winter dormancy period. During this time the roots and carnivorous leaves wither.Temperate species flower when they form their summer rosettes while tropical species flower at each rosette change.
Sarracenia is a genus comprising 8 to 11 species of North American pitcher plants. The genus belongs to the family Sarraceniaceae, which also contain the closely allied genera Darlingtonia and Heliamphora.
Sarracenia is a genus of carnivorous plants indigenous to the eastern seaboard, Texas, the Great Lakes area and southeastern Canada, with most species occurring only in the south-east United States. The plant’s leaves have evolved into a funnel in order to trap insects, digesting their prey with protease and other enzymes.
The insects are attracted by a nectar-like secretion on the lip of pitchers, as well as a combination of color and scent. Slippery footing at the pitchers’ rim, aided in at least one species by a narcotic drug lacing the nectar, causes insects to fall inside, where they die and are digested by the plant as a nutrient source.
All Sarracenia trap insects and other prey without the use of moving parts. Their traps are static and are based on a combination of lures and inescapability – typically the entrances to the traps are one-way by virtue of the highly adapted features listed above.
Most species use a combination of scent, drugged nectar, waxy deposits and gravity to topple insect prey into their pitcher. Coniine, an alkaloid drug narcotic to insects, has been discovered in the nectar-like secretions of at least S. flava. Once inside, the insect finds the footing very slippery with a waxy surface covering the walls of the pitcher.
Further down the tube, downward-pointing hairs make retreat impossible, and in the lowest region of the tube, a pool of liquid containing digestive enzymes and wetting agents quickly drowns the prey and begins digestion. The exoskeletons are usually not digested, and over the course of the summer fill up the pitcher tube.
Utricularia, commonly and collectively called the bladderworts, is a genus of carnivorous plants consisting of approximately 233 species. They occur in fresh water and wet soil as terrestrial or aquatic species across every continent except Antarctica. Utricularia are cultivated for their flowers, which are often compared with those of snapdragons and orchids, and among carnivorous plant enthusiasts.
The main part of a bladderwort plant always lies beneath the surface of its substrate. Terrestrial species sometimes produce a few photosynthetic leaf-shoots which lie unobtrusively flat against the surface of their soil, but in all species only the flowering stems rise above and are prominent. This means that the terrestrial species are generally visible only while they are in flower, although aquatic species can be observed below the surfaces of ponds and streams.
All Utricularia are carnivorous and capture small organisms by means of bladder-like traps. Terrestrial species tend to have tiny traps that feed on minute prey such as protozoa and rotifers swimming in water-saturated soil. The traps can range in size from 0.2 mm to 1.2 cm. Aquatic species, such as U. vulgaris , possess bladders that are usually larger and can feed on more substantial prey such as water fleas (Daphnia), nematodes and even fish fry, mosquito larvae and young tadpoles.
Despite their small size, the traps are extremely sophisticated. In the active traps of the aquatic species, prey brush against trigger hairs connected to the trapdoor. The bladder, when “set”, is under negative pressure in relation to its environment so that when the trapdoor is mechanically triggered, the prey, along with the water surrounding it, is swept into the bladder.
Once the bladder is full of water, the door closes again, the whole process taking only ten to fifteen thousandths of a second.Bladderworts are unusual and highly specialized plants, and the vegetative organs are not clearly separated into roots, leaves, and stems as in most other angiosperms. The bladder traps, conversely, are recognized as one of the most sophisticated structures in the plant kingdom.
The members of this genus look very much like lanky species of Drosera. However, their flowers are zygomorphic (bilaterally symmetric), which is a little different from the actinomorphic (radially symmetric) flowers of Drosera. This is not very obvious on some species, but look at the flower photograph on this page. Do you see how the anthers are bunched together a bit below the middle of the flower?
A name purportedly used for it is rainbow plant, although I have only ever heard one person use this name in conversation. It is completely goofy in my opinion, as it is supposed to note the way the gland droplets, if viewed at the correct angle with respect to the illumination source, refract light into spectral colors. This simple optical effect can be seen in Drosera, Drosophyllum, Pinguicula, grassy lawns, and freshly moistened pavement. I do not refer to such observations as “rainbow pavement”, nor will I refer to these plants by such a name.
As names go, I much prefer the simpler Byblis. It brings forth the memory of the spicy hot granddaughter (or niece, depending on the telling) of the Roman god Apollo. Byblis was most-bodacious, and made Carmen Electra look positively dull. But she made the nasty mistake of developing amorous feelings for her twin brother, Caunus. Even though this kind of thing was not completely forbidden for gods and their kin, her brother (presumably studly, although perhaps only in a quasi-effete, Justin Timberlake kind of way) spurned her. So she cried and cried and cried. And then, She was turned into a fountain.
Byblis plants are covered with sticky hairs. Prey that land on Byblis get snagged in the slime and die in the plant’s embrace. The plant does not exhibit any kind of prey-related motion; bugs just land on the plant and become stuck. Some, but not all, of the species in Byblis have been tested for digestive enzymes, and the results are in a state of mild discord.
Byblis gigantea and B. filifolia have enzymes, but Byblis liniflora does not demonstrate enzymatic activity, at least not when examined by the classic film-emulsion test. However, sensitive fluorescence tests have detected phosphatase in Byblis liniflora. In all cases so far, the enzymes are exuded by inconspicuous sessile glands.
Heliamphora is a beautiful genus of pitcher plants from the Guiana Highlands of South America. There, the Heliamphora grow on (or near) mountains, many of which are called tepuis. Temperatures on the tepui summits range between 8-20°C (46-68°F), with cold but generally frostless nights. Rain is nearly constant, with 200-400 cm (80-160 inches) annually.
These chilly rains wash loose material off the tepui-tops, so soil accumulation is rare. Because these tepuis are so geographically fragmented, evolution travels different trajectories on each mountain, and each tepui may have its own composition of unique species–33% of the tepui species occur nowhere else in the world!
It is common for people to think of Heliamphora as a genus of “primitive” pitcher plants, but I think this is an unfair characterization based on four unfair tenets. First, Heliamphora pitchers do not have the large lids typical in other pitcher plants. This doesn’t impress me, because the pitchers of Heliamphora instead have a complicated little structure called a nectar roll (or nectar spoon) that varies from species to species.
Second, Heliamphora pitchers apparently do not produce digestive enzymes. Well, neither does Darlingtonia californica but no one calls that plant primitive! Also, there is some evidence that Heliamphora tatei does produce its own enzymes. Third, for a long time photographs of Heliamphora plants in the wild and in cultivation tended to show specimens that were all green, and not very attractively pigmented.
This made them look boring. Newer photography of plants in the wild show plants of spectacular pigmentation patterns. Finally, and very silly, people have long associated tepuis with stories of “lost worlds”, frozen in time and populated with dinosaurs. Heliamphora must therefore be a primitive genus.
Heliamphora species forage using the basic pitfall strategy. Insects are attracted to the pitchers by their colorful pigmentation and, in some cases, honeylike scent. In particular, flying meals approach the nectar spoon at the top of the pitcher tube, attracted by the generously productive nectar glands there. As they feed, they court death on the treacherous surface.
Some lose the game. The inside of the pitcher is adorned with downward pointing hairs (the exact nature and distribution of these hairs varies with the species), and these hairs increase the efficiency of the pitcher’s hunting skills. The bottom of the pitcher is filled with fluid, where the prey drowns.
Digestion occurs by bacterial action, although digestive enzymes may be produced by at least Heliamphora tatei.Heliamphora pitchers have marvelous adaptations to avoid being overfilled by the excessive rainfall on the tepui-tops. The pitchers have a small pore or slit (depending upon the species) which acts as an overflow spout. No other pitcher plant genus has this feature. Heliamphora species are primitive?
There is some conflict in the reports of the frequency of prey capture. Some field researchers report almost no prey in the pitchers, while others observe plenty of captured prey. I can offer no reconciliation of these diverging reports!
The flowers of Heliamphora are surprisingly monocot-like in appearance, and have four to six tepals.
There is a lot of controversy regarding the number of species in the genus, and the ranks for the various species. Should such-and-such be a separate species, or only a variety, etc? There are, I think, three issues here which are causing problems. First, the tepuis have simply not been sufficiently explored.
They are hard to get to, hard to traverse, and permits to conduct research are practically impossible to obtain. So we have a hugely inadequate understanding of the plants that occur on the tepuis. Second, simultaneously occurring processes of hybridization and speciation on fragmented tepuis have greated an ensemble of Heliamphora populations that confound classification into distinct botanical taxa. Third, different scientists have different definitions and perspectives as to what constitutes separate species.
Cephalotus follicularis is an absolutely fabulous looking plant from southwest Australia. A pot of these bizarre little things look so grotesquely bizarre, you expect their lids to start flapping at you any second as they start singing a happy little puppet song or demand a blood sacrifice immediately (depending upon which kind of movie your life is).
Really, this rosetted plant is remarkable. Not very large—the biggest, grandest clumps of pitchers are only about 60 cm in diameter), the rosettes consist of two types of leaves. One kind is flat, a few to several cm long, and somewhat tonguelike. The other kind is dramatically transmogrified into a complex pitcher shape of similar size to the foliage leaves. (Very occasionally, mutant intermediate leaves are produced.)
The pitchers are marvels of adaptation. Flanged wings on the pitchers might function as insect highways, drawing prey up to the pitcher mouth. A lid with windows allows in light, but prevents the pitcher from overfilling with rain. It probably also helps retain prey (although, like all other lidded pitcher plants, there is no opening or closing activity associated with trapping). A peristome around the mouth is festooned with glands. Prey that fall into the pitcher find escape impossible because of the microscopic downward-pointing projections on the slippery pitcher walls, and a nasty overhanging ceiling they cannot navigate around. Each pitcher is filled with fluid, exuded by comparatively large (0.2 mm diameter) domelike glands. There is some opinion that this plant specializes in trapping ants, although field researchers often report a variety of captured prey.
Once inside, insects must contend with the dread gland patch. Ahh, the gland patch. This elongated patch near the bottom of each Picher is covered with tiny (0.02 mm diameter) glands that secrete digestive enzymes.
The common name, Albany pitcher plant, merely indicates that this plant is found near the Australian town of Albany. The Latin name translates, strangely enough, to “the sack-bearing, headed one”. Although this sounds like some horrible kind of schoolyard insult that got messed up on the delivery, it actually is a convoluted set of botanical references. The “sack” refers to the pitchers, while the “headed” refers to the shape of the flower’s anthers. Hmmm, a pretty damn strange of a strange choice of epithets, in my opinion.
The entire plant is covered with so many little bristles it has been called a “vegetable hedgehog.” This is the kind of historical oddity in which I delight.
The Nepenthes , popularly known as tropical pitcher plants or monkey cups, are a genus of carnivorous plants in the monotypic family Nepenthaceae. The genus comprises roughly 140 species, numerous natural and many cultivated hybrids. They are mostly Liana-forming plants of the Old World tropics, ranging from South China, Indonesia, Malaysia and the Philippines; westward to Madagascar (2 species) and the Seychelles (1); southward to Australia (3) and New Caledonia (1); and northward to India (1) and Sri Lanka (1).
The greatest diversity occurs on Borneo and Sumatra with many endemic species. Many are plants of hot humid lowland areas, but the majority are tropical montane plants, receiving warm days but cool to cold humid nights year round. A few are considered tropical alpine with cool days and nights near freezing. The name monkey cups refer to the fact those monkeys have been observed drinking rainwater from these plants.
Nepenthes species usually consist of a shallow root system and a prostrate or climbing stem, often several meters long and up to 15 m (49 ft) or more, and usually 1 cm (0.4 in) or less in diameter, although this may be thicker in a few species which in some species aid in climbing, protrudes from the tip of the leaf; at the end of the tendril the pitcher forms. The pitcher starts as a small bud and gradually expands to form a globe- or tube-shaped trap.
The trap contains a fluid of the plant’s own production, which may be watery or syrupy and is used to drown the prey. Research has shown that this fluid contains viscoelastic bio-polymers that may be crucial to the retention of insects within the traps of many species. The trapping efficiency of this fluid remains high, even when significantly diluted by water, as inevitably happens in wet conditions.
The lower part of the trap contains glands which absorb nutrients from captured prey. Along the upper inside part of the trap is a slick waxy coating which makes the escape of its prey nearly impossible. Surrounding the entrance to the trap is a structure called the peristome which is slippery and often quite colorful, attracting prey but offering an unsure footing. Above the peristome is a lid in many species this keeps rain from diluting the fluid within the pitcher, the underside of which may contain nectar glands which attract prey.
Nepenthe usually produce two types of pitchers, known as leaf dimorphism. Appearing near the base of the plant are the large lower traps, which typically sit on the ground. The upper or aerial pitchers are usually smaller, differently-coloured, and possess different features from the lower pitchers. These upper pitchers usually form as the plant reaches maturity and the plant grows taller.
To keep the plant steady, the upper pitchers often form a loop in the tendril, allowing it to wrap around nearby support. In some species different prey may be attracted by the two types of pitchers. This varied morphology also often makes identification of species difficult.
Prey usually consists of insects, but the largest species may occasionally catch small vertebrates, such as rats and lizards. There are even records of cultivated plants trapping small birds. Flowers occur in racemes or more rarely in panicles with male and female flowers on separate plants.
They are insect pollinated, the primary agents being flies (including blow flies, midges, and mosquitoes), moths, wasps, and butterflies. Their smell can range from sweet to musty or fungus-like. Seed is produced in a four-sided capsule which may contain 50–500 wind-distributed seeds, consisting of a central embryo and two wings, one on either side.