| Venus flytrap |
|---|
 |
| Leaf |
|
|
|---|
|
|
| Scientific classification |
|---|
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Core eudicots |
| Order: | Caryophyllales |
| Family: | Droseraceae |
| Genus: | Dionaea |
| Species: | D. muscipula |
| Binomial name |
|---|
Dionaea muscipula
Sol. ex J.Ellis 1768 |
 |
| Distribution |
| Synonyms[2] |
|---|
- Dionea Raf., spelling variant
- Dionaea corymbosa
(Raf.) Steud. (1840)
- Dionaea crinita
Sol. (1990) as synonym
- Dionaea dentata
D'Amato (1998) name published without description
- Dionaea heterodoxa
D'Amato (1998) nom.nud.
- Dionaea muscicapa
St.Hil. (1824) sphalm.typogr.
- Dionaea sensitiva
Salisb. (1796)
- Dionaea sessiliflora
(Raf.) Steud. (1840)
- Dionaea uniflora
(Raf.) Steud. (1840)
- Drosera corymbosa
Raf. (1833)
- Drosera sessiliflora
Raf. (1833)
- Drosera uniflora
Raf. (1833)
|
The
Venus flytrap (also referred to as
Venus's flytrap or
Venus' flytrap),
Dionaea muscipula, is a
carnivorous plant native to
subtropical wetlands on the
East Coast of the
United States in
North Carolina and
South Carolina.
[3] It catches its prey—chiefly
insects and
arachnids—with a trapping structure formed by the terminal portion of each of the plant's leaves, which 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 wasting energy by trapping objects with no nutritional value.
Description
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;
[4] longer leaves with robust traps are usually formed after flowering. Flytraps that have more than 7 leaves are
coloniesformed by rosettes that have divided beneath the ground.
The leaf blade is divided into two regions: a flat, heart-shaped
photosynthesis-capable
petiole, and a pair of terminal lobes hinged at the midrib, forming the trap which is the true leaf. The upper surface of these lobes contains red
anthocyanin pigments and its edges secrete
mucilage. The lobes exhibit
rapid plant movements, snapping shut when stimulated by prey. The trapping mechanism is tripped when prey contacts one of the three hair-like
trichomes that are found on the upper surface of each of the lobes. The mechanism is so highly specialized that it can distinguish between living prey and non-prey stimuli, such as falling raindrops;
[5] two trigger hairs must be touched in succession within 20 seconds of each other or one hair touched twice in rapid succession,
[5] whereupon the lobes of the trap will snap shut, typically in about one-tenth of a second.
[6] The edges of the lobes are fringed by stiff hair-like protrusions or cilia, which mesh together and prevent large prey from escaping. These protrusions, and the trigger hairs (also known as sensitive hairs) are likely
homologous with the tentacles found in this plant’s close relatives, the
sundews. Scientists have concluded that the snap trap evolved from a fly-paper trap similar to that of
Drosera.
[7]
The holes in the meshwork allow small prey to escape, presumably because the benefit that would be obtained from them would be less than the cost of digesting them. If the prey is too small and escapes, the trap will usually reopen within 12 hours. If the prey moves around in the trap, it tightens and digestion begins more quickly.
Speed of closing can vary depending on the amount of humidity, light, size of prey, and general growing conditions. The speed with which traps close can be used as an indicator of a plant's general health. Venus flytraps are not as humidity-dependent as are some other carnivorous plants, such as
Nepenthes,
Cephalotus, most
Heliamphora, and some
Drosera.
The Venus flytrap exhibits variations in petiole shape and length and whether the leaf lies flat on the ground or extends up at an angle of about 40–60 degrees. The four major forms are: 'typica', the most common, with broad decumbent petioles; 'erecta', with leaves at a 45-degree angle; 'linearis', with narrow petioles and leaves at 45 degrees; and 'filiformis', with extremely narrow or linear petioles. Except for 'filiformis', all of these can be stages in leaf production of any plant depending on season (decumbent in summer versus short versus semi-erect in spring), length of photoperiod (long petioles in spring versus short in summer), and intensity of light (wide petioles in low light intensity versus narrow in brighter light).
[citation needed]
When grown from seed, plants take around four to five years to reach maturity and will live for 20 to 30 years if cultivated in the right conditions.
[8]
|
|
Closeup of flower ( c. 20 mm in diameter) |
|
|
The species produces small, shiny black seeds
|
|
Etymology
The plant's common name refers to
Venus, the Roman goddess of love. The genus name,
Dionaea ("daughter of
Dione"), refers to the Greek goddess
Aphrodite, while the species name,
muscipula, is Latin for "mousetrap".
[9]
Historically, the plant was also known by the slang term "tipitiwitchet" or "tippity twitchet", possibly an oblique reference to the plant's resemblance to human female genitalia.
[9][10]
Carnivory
Prey selectivity
A time lapse showing Venus flytrap catching prey
Most carnivorous plants selectively feed on specific prey. This selection is due to the available prey and the type of trap used by the organism. With the Venus flytrap, prey is limited to beetles, spiders and other crawling arthropods. In fact, the
Dionaea diet is 33% ants, 30% spiders, 10% beetles, and 10% grasshoppers, with fewer than 5% flying insects.
[11] Given that
Dionaea evolved from an ancestral form of
Drosera (carnivorous plants that use a sticky trap instead of a snap trap) the reason for this evolutionary branching becomes clear. Whilst
Drosera consume smaller, aerial insects,
Dionaea consume larger terrestrial bugs. From these larger bugs,
Dionaea are able to extract more nutrients. This gives
Dionaea an evolutionary advantage over their ancestral sticky trap form.
[12]
Mechanism of trapping
Closeup of one of the hinged trigger hairs
The mechanism by which the trap snaps shut involves a complex interaction between
elasticity,
turgor and growth. The trap only shuts when the trigger hair is stimulated twice: this is to avoid inadvertent triggering of the mechanism by dust and other wind-borne debris. In the open, untripped state, the lobes are
convex (bent outwards), but in the closed state, the lobes are
concave (forming a cavity). It is the rapid flipping of this
bistable state that closes the trap,
[6] but the mechanism by which this occurs is still poorly understood. When the trigger hairs are stimulated, an
action potential (mostly involving calcium ions — see
calcium in biology) is generated, which propagates across the lobes and stimulates cells in the lobes and in the
midrib between them.
[13] It is hypothesized that there is a threshold of ion buildup for the Venus flytrap to react to stimulation.
[14] After closing, the flytrap counts additional stimulations of the trigger hairs, to five total, to start the production of digesting enzymes.
[15] The
acid growth theory states that individual cells in the outer layers of the lobes and midrib rapidly move
1H+ (
hydrogen ions) into their cell walls, lowering the
pH and loosening the extracellular components, which allows them to swell rapidly by
osmosis, thus elongating and changing the shape of the trap lobe. Alternatively, cells in the inner layers of the lobes and midrib may rapidly secrete other
ions, allowing water to follow by osmosis, and the cells to collapse. Both of these mechanisms may play a role and have some experimental evidence to support them.
[16][17]
Digestion
If the prey is unable to escape, it will continue to stimulate the inner surface of the lobes, and this causes a further growth response that forces the edges of the lobes together, eventually sealing the trap
hermetically and forming a 'stomach' in which
digestion occurs. Digestion is
catalysed by
enzymes secreted by glands in the lobes.
Digestion takes about ten days, after which the prey is reduced to a husk of
chitin. The trap then reopens, and is ready for reuse.
[20]
Evolution
The carnivorous diet is a very specialized form of
foliar feeding, and is an adaptation found in several plants that grow in nutrient-poor soil. Carnivorous traps were naturally selected to allow these organisms to compensate for the nutrient deficiencies of their harsh environments by supplementing ordinary
photosynthate with animal proteins.
[21]
The "snap trap" mechanism characteristic of
Dionaea is shared with only one other carnivorous plant genus,
Aldrovanda. For most of the 20th century, this relationship was thought to be coincidental, more precisely an example of
convergent evolution. Some phylogenetic studies even suggested that the closest living relatives of
Aldrovanda were the
sundews.
[22] It was not until 2002 that a molecular evolutionary study, by analyzing combined
nuclear and
chloroplast DNA sequences, indicated that
Dionaea and
Aldrovanda were closely related and that the snap trap mechanism evolved only once in a
common ancestor of the two genera.
[23][24]
A 2009 study
[22] presented evidence for the evolution of snap traps of
Dionaea and
Aldrovanda from a flypaper trap like
Drosera regia, based on
molecular data. The molecular and physiological data imply that
Dionaea and
Aldrovanda snap traps evolved from the flypaper traps of a common ancestor with
Drosera. Pre-adaptations to the evolution of snap traps were identified in several species of
Drosera, such as rapid leaf and tentacle movement. The model proposes that plant carnivory by snap trap evolved from the flypaper traps, driven by increasing prey size. Bigger prey provides greater nutritional value, but large insects can easily escape the sticky mucilage of flypaper traps; the evolution of snap traps would therefore prevent escape and
kleptoparasitism (theft of prey captured by the plant before it can derive benefit from it), and would also permit a more complete digestion.
[22][23]
Proposed evolutionary history
Carnivorous plants are generally herbs, and their traps the result of
primary growth. They generally do not form readily fossilizable structures such as thick bark or wood. As a result, there is no fossil evidence of the steps that might link
Dionaea and
Aldrovanda, or either genus with their common ancestor,
Drosera. Nevertheless, it is possible to infer an evolutionary history based on phylogenetic studies of both genera. Researchers have proposed a series of steps that would ultimately result in the complex snap-trap mechanism:
[22][23]
- Larger insects usually walk over the plant, instead of flying to it,[25] and are more likely to break free from sticky glands alone. Therefore, a plant with wider leaves, likeDrosera falconeri,[22] must have adapted to move the trap and its stalks in directions that maximized its chance of capturing and retaining such prey - in this particular case, longitudinally. Once adequately "wrapped", escape would be more difficult.[25]
- Evolutionary pressure then selected for plants with shorter response time, in a manner similar to Drosera burmannii or Drosera glanduligera. The faster the closing, the less reliant on the flypaper model the plant would be.
- As the trap became more and more active, the energy required to "wrap" the prey increased. Plants that could somehow differentiate between actual insects and random detritus/rain droplets would have an advantage, thus explaining the specialization of inner tentacles into trigger hairs.
- Ultimately, as the plant relied more on closing around the insect rather than gluing them to the leaf surface, the tentacles so evident in Drosera would lose their original function altogether, becoming the "teeth" and trigger hairs — an example of natural selection utilizing pre-existing structures for new functions.
- Completing the transition, the plant eventually developed the depressed digestive glands found inside the trap, rather than using the dews in the stalks, further differentiating it from genus Drosera.
Habitat
The Venus flytrap is found in
nitrogen- and phosphorus-poor environments, such as
bogs and wet savannahs. Small in stature and slow-growing, the Venus flytrap tolerates fire well, and depends on periodic burning to suppress its competition.
[26] Fire suppression threatens its future in the wild.
[27] It survives in wet sandy and peaty soils. Although it has been successfully transplanted and grown in many locales around the world, it is native only to the coastal bogs of North and South Carolina in the United States, specifically within a 60-mile radius of
Wilmington, North Carolina.
[28] One such place is North Carolina's
Green Swamp. There also appears to be a naturalized population of Venus flytraps in northern
Florida as well as an introduced population in western
Washington.
[29][30] The nutritional poverty of the soil is the reason that the plant relies on such elaborate traps: insect prey provide the nitrogen for
protein formation that the soil cannot. The Venus flytrap is not a tropical plant and can tolerate mild winters. In fact, Venus flytraps that do not go through a period of winter dormancy will weaken and die after a period of time.
[31]
Cultivation
Dionaea muscipula 'Akai Ryu', Japanese for 'Red Dragon', in cultivation
Venus flytraps are popular as cultivated plants, but have a reputation for being difficult to grow.
[4] Successfully growing these specialized plants requires recreating a close approximation to the plant's natural habitat.
Healthy Venus flytraps will produce
scapes of white flowers in
spring; however, many growers remove the flowering stems early (2–3 inches), as flowering consumes some of the plant's energy and thereby reduces the rate of trap production. If healthy plants are allowed to flower, successful pollination will result in seeds.
Plants can be propagated by seed, although seedlings take several years to mature. More commonly, they are propagated by clonal division in spring or summer.
Cultivars
Venus flytraps are by far the most commonly recognized and cultivated carnivorous plant, and they are frequently sold as houseplants. Various
cultivars (cultivated varieties) have come into the market through
tissue culture of selected genetic mutations, and these plants are raised in large quantities for commercial markets.
Conservation
The species is classified as "vulnerable" by the
National Wildlife Federation.
[32] In 2015, there were estimated to be fewer than 33,000 plants in the wild, all within 75 miles (121 km) of the city of Wilmington, North Carolina, and all on sites owned by
The Nature Conservancy, the North Carolina state government, or the US military.
[33]
In 2014, the state of North Carolina passed legislation to classify the theft of naturally growing Venus flytraps in some counties as a felony.
[34]
In alternative medicine
.svg)
