Bladderwort
Encyclopedia
Utricularia, commonly and collectively called the bladderworts, is a genus of carnivorous plant
s consisting of approximately 233 species (precise counts differ based on classification opinions; one recent publication lists 215 species). They occur in fresh water and wet soil as terrestrial or aquatic species across every continent except Antarctica. Utricularia are cultivated for their flower
s, which are often compared with those of snapdragon
s and orchids, and among carnivorous plant enthusiasts.
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 rotifer
s 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
(common bladderwort
), possess bladders that are usually larger and can feed on more substantial prey such as water fleas (Daphnia
), nematode
s and even fish fry, mosquito
larva
e and young tadpole
s. 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 root
s, leaves
, and stem
s as in most other angiosperms. The bladder traps, conversely, are recognized as one of the most sophisticated structures in the plant
kingdom.
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.
The name bladderwort refers to the bladder-like traps. The generic name Utricularia is similarly derived from the Latin utriculus, a word which has many related meanings but which most commonly means wine flask or leather bottle. The aquatic members of the genus have the largest and most obvious bladders, and these were initially thought to be flotation devices before their carnivorous nature was discovered.
Flowers are the only part of the plant clear of the underlying soil or water. They are usually produced at the end of thin, often vertical inflorescence
s. They can range in size from 2 mm to 10 cm wide, and have two asymmetric labiate (unequal, lip-like) petals, the lower usually significantly larger than the upper. They can be of any colour, or of many colours, and are similar in structure to the flowers of a related carnivorous genus, Pinguicula
.
The flowers of aquatic varieties like U. vulgaris are often described as similar to small yellow snapdragon
s, and the Australian species U. dichotoma
can produce the effect of a field full of violet
s on nodding stems. The epiphytic species of South America, however, are generally considered to have the showiest, as well as the largest, flowers. It is these species that are frequently compared with orchids.
Certain plants in particular seasons might produce closed, self-pollinating (cleistogamous) flowers; but the same plant or species might produce open, insect-pollinated flowers elsewhere or at a different time of year, and with no obvious pattern. Sometimes, individual plants have both types of flower at the same time: aquatic species such as U. dimorphantha and U. geminiscapa
, for example, usually have open flowers riding clear of the water and one or more closed, self-pollinating flowers beneath the water. Seeds are numerous and small and for the majority of species are as small as 0.2 mm to 1 mm long.
, Drosera and others–in very wet areas where continuously moving water removes most soluble minerals from the soil.
About 80% of the species are terrestrial, and most inhabit waterlogged or wet soils, where their tiny bladders can be permanently exposed to water in the substrate. Frequently they will be found in marshy areas where the water table
is very close to the surface. Most of the terrestrial species are tropical, although they occur worldwide.
Approximately 20% of the species are aquatic. Most of these drift freely over the surface of ponds and other still, muddy-bottomed waters and only protrude above the surface when flowering, although a few species are lithophytic
and adapted to rapidly moving streams or even waterfalls. The plants are usually found in acidic waters, but they are quite capable of growing in alkaline waters and would very likely do so were it not for the higher level of competition from other plants in such areas. Utricularia vulgaris is an aquatic species and grows into branching rafts with individual stolons up to one metre or longer in ponds and ditches throughout Eurasia
.
Some South American tropical species are epiphyte
s, and can be found growing in wet moss and spongy bark on trees in rainforests, or even in the watery leaf-rosettes of other epiphytes such as various Tillandsia
(a type of bromeliad) species. Rossette-forming epiphytes such as U. nelumbifolia
put out runners, searching for other nearby bromeliads to colonise.
The plants are as highly adapted in their methods of surviving seasonally inclement conditions as they are in their structure and feeding habits. Temperate
perennials
can require a winter period in which they die back each year, and they will weaken in cultivation if they are not given it; tropical and warm-temperate species, on the other hand, require no dormancy. Floating bladderworts in cold temperate zones such as the UK and Siberia can produce winter buds called turions at the extremities of their stems: as the autumnal light fails and growth slows down, the main plant may rot away or be killed by freezing conditions, but the turions will separate and sink to the bottom of the pond to rest beneath the coming ice until the spring, when they will return to the surface and resume growth. Many Australian species will grow only during the wet season, reducing themselves to tubers only 10 mm long to wait out the dry season. Other species are annual
, returning from seed each year.
and Francis Ernest Lloyd, agree that the vacuum-driven bladders of Utricularia are the most sophisticated carnivorous trapping mechanism to be found anywhere in the plant kingdom
. The bladders are usually shaped similarly to broad beans
(though they come in various shapes) and are to be found attached to the submerged stolons by slender stalks.
The bladder walls are very thin and transparent, but are sufficiently inflexible to maintain the bladder's shape despite the vacuum created within. The entrance, or 'mouth', of the trap is a circular or oval flap whose upper half is joined to the body of the trap by very flexible, yielding cells which form an effective hinge. The door rests on a platform formed by the thickening of the bladder wall immediately underneath. A soft but substantial membrane called the velum stretches in a curve around the middle of this platform, and helps seal the door. A second band of springy cells cross the door just above its lower edge, and provide the flexibility for the bottom of the door to become a bendable 'lip' which can make a perfect seal with the velum.
The outer cells of the whole trap excrete mucilage
and under the door this is produced in greater quantities and contains sugars. The mucilage certainly contributes towards the seal, and the sugars may help to attract prey.
Terrestrial species generally have tiny traps (sometimes as small as 0.2 mm) with a broad beak-like structure extending and curving down over the entrance; this forms a passageway to the trapdoor and may help prevent the trapping and ingestion of inorganic particles. Aquatic species tend to have larger bladders (up to 1.2 cm), and the mouth of the trap is usually surrounded not by a beak but by branching antennae, which serve both to guide prey animals to the trap entrance and to fend the trap mouth away from larger bodies which might trigger the mechanism needlessly. Epiphytic species have unbranched antennae which curve in front of the mouth and probably serve the same purpose, although it has been observed that they are also capable of holding a pocket of water in front of the mouth by capillary action, and that this assists with the trapping action.
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The trapping mechanism of Utricularia is purely mechanical; no reaction from the plant (irritability) is required in the presence of prey, in contrast with the triggered mechanisms employed by Venus Flytraps (Dionaea), waterwheels (Aldrovanda
), and many sundews (Drosera). The only active mechanism involved is the constant pumping out of water through the bladder walls by active transport
.
As water is pumped out, the bladder's walls are sucked inwards by the partial vacuum created, and any dissolved material inside the bladder will become more concentrated. The sides of the bladder bend inwards, storing potential energy like a spring. Eventually, no more water can be extracted, and the bladder trap is 'fully set' (technically, osmotic pressure rather than physical pressure is the limiting factor).
Extending outwards from the bottom of the trapdoor are several long bristle-stiff protuberances that are sometimes referred to as trigger hairs or antennae but which have no similarity to the sensitive triggers found in Dionaea and Aldrovanda. In fact, these bristles are simply levers. The suction force exerted by the primed bladder on the door is resisted by the adhesion of its flexible bottom against the soft-sealing velum. The equilibrium depends quite literally on a hair trigger, and the slightest touch to one of the lever hairs will deform the flexible door lip enough to create a tiny gap, breaking the seal.
Once the seal is disturbed, the bladder walls instantly spring back to a more rounded shape; the door flies open and a column of water is sucked into the bladder. The animal which touched the lever, if small enough, is inevitably drawn in, and as soon as the trap is filled, the door resumes its closed position—the whole operation being completed in as little as one-hundredth of a second.
Once inside, the prey will be dissolved by digestive secretions. This generally occurs within a few hours, although some protozoa appear to be highly resistant and have been observed to live for several days inside the trap. All the time, the trap walls continue to pump out water, and the bladder can be ready for its next capture in as little as 15 to 30 minutes.
s, for example).
He tested the role of the velum
by showing that the trap will never set if small cuts are made to it; and showed that the excretion of water can be continued under all conditions likely to be found in the natural environment, but can be prevented by driving the osmotic pressure in the trap beyond normal limits by the introduction of glycerine.
Prior to Lloyd, several authors had reported this phenomenon and had attempted to explain it by positing that creatures caught by the tail repeatedly set off the trap as they thrash about in an attempt to escape—even as their tails are actively digested by the plant. Lloyd, however, demonstrated that the plant is quite capable of ingestion by stages without the need of multiple stimuli.
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He produced suitable artificial "prey" for his experiments by stirring albumen (egg white) into hot water and selecting shreds of an appropriate length and thickness. When caught by one end, the strand would gradually be drawn in, sometimes in sudden jumps, and at other times by a slow and continuous motion. Strands of albumen would often be fully ingested in as little as twenty minutes.
Mosquito larvae, caught by the tail, would be engulfed bit by bit. A typical example given by Lloyd showed that a larva of a size at the upper limit of what the trap could manage would be ingested stage by stage over the course of about twenty-four hours; but that the head, being rigid, would often prove too large for the mouth of the trap and would remain outside, plugging the door. When this happened, the trap evidently formed an effective seal with the head of the larva as it could still excrete water and become flattened, but it would nevertheless die within about ten days "evidently due to overfeeding".
Softer-bodied prey of the same size such as small tadpoles could be ingested completely, because they have no rigid parts and the head, although capable of plugging the door for a time, will soften and yield and finally be drawn in.
Very thin strands of albumen could be soft and fine enough to allow the trapdoor to close completely; these would not be drawn in any further unless the trigger hairs were indeed stimulated again. On the other hand, a human hair, finer still but relatively hard and unyielding, could prevent a seal being formed; these would prevent the trap from resetting at all due to leakage of water.
Lloyd concluded that the sucking action produced by the excretion of water from the bladder was sufficient to draw larger soft-bodied prey into the trap without the need for a second or further touch to the trigger levers. An animal long enough not to be fully engulfed upon first springing the trap, but thin and soft enough to allow the door to return fully to its set position, would indeed be left partly outside the trap until it or another body triggered the mechanism once again. However, the capture of hard bodies not fully drawn into the trap would prevent its further operation.
Utricularia is the largest genus of carnivorous plants. It is one of the three genera that make up the Bladderwort family (Lentibulariaceae
), along with the butterworts
(Pinguicula) and corkscrew plants
(Genlisea).
This genus was considered to have 250 species until Peter Taylor reduced the number to 214 in his exhaustive study The Genus Utricularia: a taxonomic monograph, published by HMSO
(1989). Taylor's classification is now generally accepted with modifications based on phylogenetic studies (see below).
The genus Polypompholyx, the pink petticoats, contained just two species of carnivorous plant
, Polypompholyx tenella and Polypompholyx multifida, previously distinguished from the otherwise similar genus Utricularia by their possession of four calyx lobes rather than two. The genus has now been subsumed into Utricularia.
The genus Biovularia contained the species Biovularia olivacea (also known as B. brasiliensis or B. minima) and Biovularia cymbantha. The genus has been subsumed into Utricularia.
shows the relationship between various subgenera and sections. It summarizes the results of two studies (Jobson et al. 2003; Müller et al. 2004), following Müller et al. 2006. Since the sections Aranella and Vesiculina are polyphyletic, they show up multiple times in the cladogram (*). Some monotypic sections have not been included in the study, so that their place in this system is unclear. Sections that are not included below are Candollea, Chelidon, Choristothecae
, Kamienskia
, Martinia, Meionula
, Mirabiles
, Oliveria, Setiscapella
, Sprucea, Steyermarkia
, and Stylotheca in subgenus Utricularia; Minutae in subgenus Bivalvaria; and Tridentaria in subgenus Polypompholyx.
Carnivorous plant
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...
s consisting of approximately 233 species (precise counts differ based on classification opinions; one recent publication lists 215 species). They occur in fresh water and wet soil as terrestrial or aquatic species across every continent except Antarctica. Utricularia are cultivated for their flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s, which are often compared with those of snapdragon
SnapDragon
SnapDragon is a contemporary jazz band based in San Antonio, Texas. The group released their debut CD, "Stealing a Moment" on Humbug Records in 2008, and the 10-song CD soon broke the Top 100 in U.S radio airplay...
s and orchids, and among carnivorous plant enthusiasts.
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
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
and rotifer
Rotifer
The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...
s 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
Utricularia vulgaris
Utricularia vulgaris is an aquatic species of bladderwort found in Asia and Europe. The plant is a free-floating and does not put down roots. Stems can attain lengths of over one metre in a single growing season, but die back and form turions in winter...
(common bladderwort
Common bladderwort
Common bladderwort may refer to these species:*Utricularia macrorhiza, in North America and eastern temperate Asia*Utricularia vulgaris, in Asia and Europe...
), possess bladders that are usually larger and can feed on more substantial prey such as water fleas (Daphnia
Daphnia
Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
), nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s and even fish fry, mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e and young tadpole
Tadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
s. 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 root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s, leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, and stem
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...
s as in most other angiosperms. The bladder traps, conversely, are recognized as one of the most sophisticated structures in the plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
kingdom.
Physical description
Plant structure
Most species form long, thin, sometimes branching stems or stolons beneath the surface of their substrate, whether that be pond water or dripping moss in the canopy of a tropical rainforest. To these stolons are attached both the bladder traps and photosynthetic leaf-shoots, and in terrestrial species the shoots are thrust upward through the soil into the air or along the surface.The name bladderwort refers to the bladder-like traps. The generic name Utricularia is similarly derived from the Latin utriculus, a word which has many related meanings but which most commonly means wine flask or leather bottle. The aquatic members of the genus have the largest and most obvious bladders, and these were initially thought to be flotation devices before their carnivorous nature was discovered.
Flowers and reproduction
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
s. They can range in size from 2 mm to 10 cm wide, and have two asymmetric labiate (unequal, lip-like) petals, the lower usually significantly larger than the upper. They can be of any colour, or of many colours, and are similar in structure to the flowers of a related carnivorous genus, Pinguicula
Pinguicula
The butterworts are a group of carnivorous plants comprising the genus Pinguicula. Members of this genus 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...
.
The flowers of aquatic varieties like U. vulgaris are often described as similar to small yellow snapdragon
SnapDragon
SnapDragon is a contemporary jazz band based in San Antonio, Texas. The group released their debut CD, "Stealing a Moment" on Humbug Records in 2008, and the 10-song CD soon broke the Top 100 in U.S radio airplay...
s, and the Australian species U. dichotoma
Utricularia dichotoma
Utricularia dichotoma, commonly known as fairy aprons, is a variable, perennial species of terrestrial bladderwort. The specific epithet is Latin for "dividing into pairs" and refers to the double arrangement of flowers which this species often displays.- Morphology :Utricularia dichotoma is a low...
can produce the effect of a field full of violet
Violet (plant)
Viola is a genus of flowering plants in the violet family Violaceae, with around 400–500 species distributed around the world. Most species are found in the temperate Northern Hemisphere; however, viola species are also found in widely divergent areas such as Hawaii, Australasia, and the Andes in...
s on nodding stems. The epiphytic species of South America, however, are generally considered to have the showiest, as well as the largest, flowers. It is these species that are frequently compared with orchids.
Certain plants in particular seasons might produce closed, self-pollinating (cleistogamous) flowers; but the same plant or species might produce open, insect-pollinated flowers elsewhere or at a different time of year, and with no obvious pattern. Sometimes, individual plants have both types of flower at the same time: aquatic species such as U. dimorphantha and U. geminiscapa
Utricularia geminiscapa
Utricularia geminiscapa, the hiddenfruit bladderwort, is a perennial, medium-sized species of aquatic bladderwort. This species occurs naturally in the northeastern USA and Canada with one record from British Columbia in Western Canada...
, for example, usually have open flowers riding clear of the water and one or more closed, self-pollinating flowers beneath the water. Seeds are numerous and small and for the majority of species are as small as 0.2 mm to 1 mm long.
Distribution and habitat
Utricularia can survive almost anywhere where there is fresh water for at least part of the year; only Antarctica and some oceanic islands have no native species. The greatest species diversity for the genus is seen in South America, with Australia coming a close second. In common with most carnivorous plants, they grow in moist soils which are poor in dissolved minerals, where their carnivorous nature gives them a competitive advantage; terrestrial varieties of Utricularia can frequently be found alongside representatives of the carnivorous genera–SarraceniaSarracenia
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....
, Drosera and others–in very wet areas where continuously moving water removes most soluble minerals from the soil.
About 80% of the species are terrestrial, and most inhabit waterlogged or wet soils, where their tiny bladders can be permanently exposed to water in the substrate. Frequently they will be found in marshy areas where the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
is very close to the surface. Most of the terrestrial species are tropical, although they occur worldwide.
Approximately 20% of the species are aquatic. Most of these drift freely over the surface of ponds and other still, muddy-bottomed waters and only protrude above the surface when flowering, although a few species are lithophytic
Lithophyte
Lithophytes are a type of plant that grows in or on rocks. Lithophytes feed off moss, nutrients in rain water, litter, and even their own dead tissue....
and adapted to rapidly moving streams or even waterfalls. The plants are usually found in acidic waters, but they are quite capable of growing in alkaline waters and would very likely do so were it not for the higher level of competition from other plants in such areas. Utricularia vulgaris is an aquatic species and grows into branching rafts with individual stolons up to one metre or longer in ponds and ditches throughout Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
.
Some South American tropical species are epiphyte
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...
s, and can be found growing in wet moss and spongy bark on trees in rainforests, or even in the watery leaf-rosettes of other epiphytes such as various Tillandsia
Tillandsia
Tillandsia is a genus of around 540 species in the Bromeliad family , found in the forests, mountains, and deserts, of Central and South America, and Mexico and the southern United States in North America....
(a type of bromeliad) species. Rossette-forming epiphytes such as U. nelumbifolia
Utricularia nelumbifolia
Utricularia nelumbifolia is a large perennial aquatic carnivorous plant that belongs to the genus Utricularia. U. nelumbifolia, an epiphytic species, is endemic to Brazil. It was originally published and described by George Gardner in 1842...
put out runners, searching for other nearby bromeliads to colonise.
The plants are as highly adapted in their methods of surviving seasonally inclement conditions as they are in their structure and feeding habits. Temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
perennials
Perennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
can require a winter period in which they die back each year, and they will weaken in cultivation if they are not given it; tropical and warm-temperate species, on the other hand, require no dormancy. Floating bladderworts in cold temperate zones such as the UK and Siberia can produce winter buds called turions at the extremities of their stems: as the autumnal light fails and growth slows down, the main plant may rot away or be killed by freezing conditions, but the turions will separate and sink to the bottom of the pond to rest beneath the coming ice until the spring, when they will return to the surface and resume growth. Many Australian species will grow only during the wet season, reducing themselves to tubers only 10 mm long to wait out the dry season. Other species are annual
Annual plant
An annual plant is a plant that usually germinates, flowers, and dies in a year or season. True annuals will only live longer than a year if they are prevented from setting seed...
, returning from seed each year.
Carnivory
Physical description of the trap
Authorities on the genus, such as botanists Peter TaylorPeter Taylor (botanist)
Peter Geoffrey Taylor was a British botanist who worked at Royal Botanic Gardens, Kew throughout his career in botany. Taylor was born in 1926 and joined the staff of the herbarium at Kew in 1948. He published his first new species, Utricularia pentadactyla, in 1954...
and Francis Ernest Lloyd, agree that the vacuum-driven bladders of Utricularia are the most sophisticated carnivorous trapping mechanism to be found anywhere in the plant kingdom
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
. The bladders are usually shaped similarly to broad beans
Vicia faba
This article refers to the Broad Bean plant. For Broadbean the company, see Broadbean, Inc.Vicia faba, the Broad Bean, Fava Bean, Field Bean, Bell Bean or Tic Bean, is a species of bean native to north Africa and southwest Asia, and extensively cultivated elsewhere. A variety is provisionally...
(though they come in various shapes) and are to be found attached to the submerged stolons by slender stalks.
The bladder walls are very thin and transparent, but are sufficiently inflexible to maintain the bladder's shape despite the vacuum created within. The entrance, or 'mouth', of the trap is a circular or oval flap whose upper half is joined to the body of the trap by very flexible, yielding cells which form an effective hinge. The door rests on a platform formed by the thickening of the bladder wall immediately underneath. A soft but substantial membrane called the velum stretches in a curve around the middle of this platform, and helps seal the door. A second band of springy cells cross the door just above its lower edge, and provide the flexibility for the bottom of the door to become a bendable 'lip' which can make a perfect seal with the velum.
The outer cells of the whole trap excrete mucilage
Mucilage
Mucilage is a thick, gluey substance produced by most plants and some microorganisms. It is a polar glycoprotein and an exopolysaccharide.It occurs in various parts of nearly all classes of plant, usually in relatively small percentages, and is frequently associated with other substances, such as...
and under the door this is produced in greater quantities and contains sugars. The mucilage certainly contributes towards the seal, and the sugars may help to attract prey.
Terrestrial species generally have tiny traps (sometimes as small as 0.2 mm) with a broad beak-like structure extending and curving down over the entrance; this forms a passageway to the trapdoor and may help prevent the trapping and ingestion of inorganic particles. Aquatic species tend to have larger bladders (up to 1.2 cm), and the mouth of the trap is usually surrounded not by a beak but by branching antennae, which serve both to guide prey animals to the trap entrance and to fend the trap mouth away from larger bodies which might trigger the mechanism needlessly. Epiphytic species have unbranched antennae which curve in front of the mouth and probably serve the same purpose, although it has been observed that they are also capable of holding a pocket of water in front of the mouth by capillary action, and that this assists with the trapping action.
Trapping mechanism
Aldrovanda
Aldrovanda is a genus of carnivorous plants encompassing one extant species and numerous extinct taxa. The genus is named in honor of the Italian naturalist Ulisse Aldrovandi, the founder of the Botanical Garden of Bologna, Orto Botanico dell'Università di Bologna.The extinct species are known...
), and many sundews (Drosera). The only active mechanism involved is the constant pumping out of water through the bladder walls by active transport
Active transport
Active transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
.
As water is pumped out, the bladder's walls are sucked inwards by the partial vacuum created, and any dissolved material inside the bladder will become more concentrated. The sides of the bladder bend inwards, storing potential energy like a spring. Eventually, no more water can be extracted, and the bladder trap is 'fully set' (technically, osmotic pressure rather than physical pressure is the limiting factor).
Extending outwards from the bottom of the trapdoor are several long bristle-stiff protuberances that are sometimes referred to as trigger hairs or antennae but which have no similarity to the sensitive triggers found in Dionaea and Aldrovanda. In fact, these bristles are simply levers. The suction force exerted by the primed bladder on the door is resisted by the adhesion of its flexible bottom against the soft-sealing velum. The equilibrium depends quite literally on a hair trigger, and the slightest touch to one of the lever hairs will deform the flexible door lip enough to create a tiny gap, breaking the seal.
Once the seal is disturbed, the bladder walls instantly spring back to a more rounded shape; the door flies open and a column of water is sucked into the bladder. The animal which touched the lever, if small enough, is inevitably drawn in, and as soon as the trap is filled, the door resumes its closed position—the whole operation being completed in as little as one-hundredth of a second.
Once inside, the prey will be dissolved by digestive secretions. This generally occurs within a few hours, although some protozoa appear to be highly resistant and have been observed to live for several days inside the trap. All the time, the trap walls continue to pump out water, and the bladder can be ready for its next capture in as little as 15 to 30 minutes.
Lloyd's experiments
In the 1940s Francis Ernest Lloyd conducted extensive experiments with carnivorous plants, including Utricularia, and settled many points which had previously been the subject of conjecture. He proved that the mechanism of the trap was purely mechanical by both killing the trigger hairs with iodine and subsequently showing that the response was unaffected, and by demonstrating that the trap could be made ready to spring a second (or third) time immediately after being set off if the bladder's excretion of water were helped by a gentle squeeze; in other words, the delay of at least fifteen minutes between trap springings is due solely to the time needed to excrete water, and the triggers need no time to recover irritability (unlike the reactive trigger hairs of Venus FlytrapVenus 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...
s, for example).
He tested the role of the velum
Velum
Velum may refer to:* Superior medullary velum, part of the nervous system that stretches between parts of the brain* Veil , the veil-like membrane of immature mushrooms extending from the margin of the cap to the stem and torn by growth...
by showing that the trap will never set if small cuts are made to it; and showed that the excretion of water can be continued under all conditions likely to be found in the natural environment, but can be prevented by driving the osmotic pressure in the trap beyond normal limits by the introduction of glycerine.
The ingestion of larger prey
Lloyd devoted several studies to the possibility, often recounted but never previously accounted for under scientific conditions, that Utricularia can consume larger prey such as young tadpoles and mosquito larvae by catching them by the tail, and ingesting them bit by bit.Prior to Lloyd, several authors had reported this phenomenon and had attempted to explain it by positing that creatures caught by the tail repeatedly set off the trap as they thrash about in an attempt to escape—even as their tails are actively digested by the plant. Lloyd, however, demonstrated that the plant is quite capable of ingestion by stages without the need of multiple stimuli.
Mosquito larvae, caught by the tail, would be engulfed bit by bit. A typical example given by Lloyd showed that a larva of a size at the upper limit of what the trap could manage would be ingested stage by stage over the course of about twenty-four hours; but that the head, being rigid, would often prove too large for the mouth of the trap and would remain outside, plugging the door. When this happened, the trap evidently formed an effective seal with the head of the larva as it could still excrete water and become flattened, but it would nevertheless die within about ten days "evidently due to overfeeding".
Softer-bodied prey of the same size such as small tadpoles could be ingested completely, because they have no rigid parts and the head, although capable of plugging the door for a time, will soften and yield and finally be drawn in.
Very thin strands of albumen could be soft and fine enough to allow the trapdoor to close completely; these would not be drawn in any further unless the trigger hairs were indeed stimulated again. On the other hand, a human hair, finer still but relatively hard and unyielding, could prevent a seal being formed; these would prevent the trap from resetting at all due to leakage of water.
Lloyd concluded that the sucking action produced by the excretion of water from the bladder was sufficient to draw larger soft-bodied prey into the trap without the need for a second or further touch to the trigger levers. An animal long enough not to be fully engulfed upon first springing the trap, but thin and soft enough to allow the door to return fully to its set position, would indeed be left partly outside the trap until it or another body triggered the mechanism once again. However, the capture of hard bodies not fully drawn into the trap would prevent its further operation.
Species
- For a complete list, please see the separate article List of Utricularia species.
Utricularia is the largest genus of carnivorous plants. It is one of the three genera that make up the Bladderwort family (Lentibulariaceae
Lentibulariaceae
Lentibulariaceae is a family of carnivorous plants containing three genera, Genlisea, the corkscrew plants, Pinguicula, the butterworts, and Utricularia, the bladderworts....
), along with the butterworts
Pinguicula
The butterworts are a group of carnivorous plants comprising the genus Pinguicula. Members of this genus 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...
(Pinguicula) and corkscrew plants
Genlisea
Genlisea is a genus of carnivorous plants also known as corkscrew plants. The 21 species grow in wet terrestrial to semi-aquatic environments distributed throughout Africa and Central and South America. The plants use highly modified underground leaves to attract, trap and digest minute...
(Genlisea).
This genus was considered to have 250 species until Peter Taylor reduced the number to 214 in his exhaustive study The Genus Utricularia: a taxonomic monograph, published by HMSO
Office of Public Sector Information
The Office of Public Sector Information is the body responsible for the operation of Her Majesty's Stationery Office and of other public information services of the United Kingdom...
(1989). Taylor's classification is now generally accepted with modifications based on phylogenetic studies (see below).
The genus Polypompholyx, the pink petticoats, contained just two species of carnivorous plant
Carnivorous plant
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...
, Polypompholyx tenella and Polypompholyx multifida, previously distinguished from the otherwise similar genus Utricularia by their possession of four calyx lobes rather than two. The genus has now been subsumed into Utricularia.
The genus Biovularia contained the species Biovularia olivacea (also known as B. brasiliensis or B. minima) and Biovularia cymbantha. The genus has been subsumed into Utricularia.
Phylogenetics
The following cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
shows the relationship between various subgenera and sections. It summarizes the results of two studies (Jobson et al. 2003; Müller et al. 2004), following Müller et al. 2006. Since the sections Aranella and Vesiculina are polyphyletic, they show up multiple times in the cladogram (*). Some monotypic sections have not been included in the study, so that their place in this system is unclear. Sections that are not included below are Candollea, Chelidon, Choristothecae
Utricularia sect. Choristothecae
Utricularia sect. Choristothecae is a section in the genus Utricularia. The two species in this section are very small rheophytic carnivorous plants that were formally included in section Avesicaria but were reassigned to their own section by Peter Taylor in 1989...
, Kamienskia
Utricularia sect. Kamienskia
Utricularia sect. Kamienskia is a section in the genus Utricularia. The two species in this section are very small bryophilous lithophytic carnivorous plants. Peter Taylor originally described and published the section and its single species, Utricularia peranomala, in 1986. In 2007, Guang Wan Hu...
, Martinia, Meionula
Utricularia sect. Meionula
Utricularia sect. Meionula is a section in the genus Utricularia. The four species in this section are small terrestrial carnivorous plants native to Southeast Asia and Australia. Constantine Samuel Rafinesque originally published some of the species in this section under two genera, Meionula and...
, Mirabiles
Utricularia sect. Mirabiles
Utricularia sect. Mirabiles is a section in the genus Utricularia. The two species in this section are small or medium sized rheophytic carnivorous plants. Peter Taylor originally described and published the section in 1989, splitting the two species off from section Avesicaria on the basis of the...
, Oliveria, Setiscapella
Utricularia sect. Setiscapella
Utricularia sect. Setiscapella is a section in the genus Utricularia that contains small or medium-sized terrestrial or subaquatic species. Most plants in this section are endemic to Central and South America with the exceptions of Utricularia stanfieldii, which is endemic to Africa, and...
, Sprucea, Steyermarkia
Utricularia sect. Steyermarkia
Utricularia sect. Steyermarkia is a section in the genus Utricularia. The three species in this section are small lithophyte carnivorous plants native to South America. Both U. aureomaculata and U. steyermarkii were previously included in U. sect...
, and Stylotheca in subgenus Utricularia; Minutae in subgenus Bivalvaria; and Tridentaria in subgenus Polypompholyx.