Drosera, commonly known as the sundews, comprise one of the largest
generaIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of
carnivorous plantCarnivorous 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, with at least 194
speciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. These members of the family
DroseraceaeDroseraceae is the botanical name for a family of flowering plants. The family is also known under its common name, the sundew family.It consists of carnivorous plants: besides the sundews, the genus Drosera, it also contains the even more-famous Venus fly trap Dionaea muscipula...
lure, capture, and digest insects using stalked
mucilaginousMucilage 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...
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.
Both the botanical name (from the
GreekAncient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
δρόσος: "drosos" = "dew, dewdrops") as well as the English common name (sundew, derived from
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
ros solis, meaning "dew of the sun") refer to the glistening drops of
mucilageMucilage 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...
at the tip of each
tentacleA tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
that resemble drops of morning
dew[Image:Dew on a flower.jpg|right|220px|thumb|Some dew on an iris in Sequoia National Park]]Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening...
.
Characteristics
Sundews are
perennialA 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...
(or rarely
annualAn 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...
)
herbaceous plantA herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...
s, forming prostrate or upright rosettes between 1 centimeter (0.4 in) and 1 meter (39 in) in height, depending on the species. Climbing species form scrambling stems which can reach much longer lengths, up to 3 meters (10 ft) in the case of
D. erythrogyneDrosera erythrogyne is a scrambling or climbing perennial tuberous species in the genus Drosera that is endemic to Western Australia. It grows in soils that are peat-sand to loam and occurs in an area along the southern Western Australian coast west of Albany in swamps or near granite outcrops. It...
. Sundews have been shown to be able to achieve a lifespan of 50 years. The genus is so specialized for
nutrientA nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
uptake through its carnivorous behavior that the pygmy sundew is missing the enzymes (
nitrate reductaseNitrate reductases are molybdoenzymes that reduce nitrate to nitrite .* Eukaryotic nitrate reductases are part of the sulfite oxidase family of molybdoenzymes....
in particular ) that plants normally use for the uptake of earth-bound nitrates.
Habit
The genus can be divided into several growth forms:
- Temperate Sundews: These species form a tight cluster of unfurled leaves called a hibernaculum
Hibernaculum is the term often applied to a winter bud of certain aquatic plants, such as the bladderworts . The buds are heavier than water, and, being developed at the approach of cold weather, they become detached, sink to the bottom of the pond, and thus survive the winter...
in a winter dormancy period (= Hemicryptophyte). All of the North American and European species belong to this group. Drosera arcturi from Australia (including Tasmania) and New Zealand is another temperate species that dies back to a horn-shaped hibernaculum.
- Subtropical Sundews: These species maintain vegetative growth year-round under uniform or nearly uniform climatic conditions.
- Pygmy Sundews: A group of roughly 40 Australian species, they are distinguished by miniature growth, the formation of gemmae
A gemma is a single cell, or a mass of cells, or a modified bud of tissue, that detaches from the parent and develops into a new individual. This type of asexual reproduction is referred to as fragmentation. It is a means of asexual propagation in plants...
for asexual reproductionAsexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
, and dense formation of hairs in the crown center. These hairs serve to protect the plants from Australia's intense summer sun. Pygmy sundews form the subgenus Bryastrum.
- Tuberous Sundews: Nearly 50 Australian species that form an underground tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
in order to survive the extremely dry summers of their habitat, re-emerging in the autumn. These so-called tuberous sundews can be further divided into two groups, those that form rosettes and those that form climbing or scrambling stems. Tuberous sundews comprise the subgenus ErgaleiumDrosera subg. Ergaleium, collectively known as the tuberous sundews, is a subgenus of three sections of tuberous species in the genus Drosera...
.
- Petiolaris Complex: A group of tropical Australian species which live in constantly warm but irregularly wet conditions. Several of the 14 species that comprise this group have developed special strategies to cope with the alternately drier conditions. Many species, for example, have petiole
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
s densely covered in trichomeTrichomes are fine outgrowths or appendages on plants and certain protists. These are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae.- Algal trichomes :...
s, which maintain a sufficiently humid environment and serve as an increased condensationCondensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
surface for morning dew. The petiolaris complex comprises the subgenus LasiocephalaDrosera subg. Lasiocephala, sometimes collectively known as the petiolaris-complex, is a subgenus of 14 species in the genus Drosera. These species are distinguished by their subpeltate to peltate lamina....
.
Although they do not form a single strictly defined growth form, a number of species are often put together in a further group:
- Queensland Sundews: A small group of three species (D. adelae
Drosera adelae, commonly known as the lance-leaved sundew or the Adelaide sundew, is a carnivorous plant in the genus Drosera that is endemic to Queensland, Australia.-Description:...
, D. schizandraDrosera schizandra is a species of Drosera found in Queensland, Australia.-External links:...
and D. proliferaDrosera prolifera is a species of Drosera found in Queensland, Australia.-External links:...
), all native to highly humid habitats in the dim understories of the Australian rainforest.
Leaves and carnivory
Sundews are characterised by the glandular tentacles, topped with sticky secretions, that cover their
laminaeA 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....
. The trapping and digestion mechanism usually employs two types of glands: stalked glands that secrete sweet mucilage to attract and ensnare insects and enzymes to digest them, and
sessileIn botany, sessility is a characteristic of plants whose flowers or leaves are borne directly from the stem or peduncle, and thus lack a petiole or pedicel...
glandA gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
s that absorb the resulting nutrient soup (the latter glands are missing in some species, such as
D. erythrorhizaDrosera erythrorhiza, the red ink sundew, is a perennial tuberous species in the carnivorous plant genus Drosera that is endemic to Western Australia. It grows in a rosette and is distinguished from the other species in section Erythrorhiza by its many-flowered cymose inflorescences with up to 50...
). Small prey, mainly consisting of insects, are attracted by the sweet secretions of the peduncular glands. Upon touching these, the prey become entrapped by sticky mucilage which prevents their progress or escape. Eventually, the prey either succumb to death through exhaustion or through asphyxiation as the mucilage envelops them and clogs their
spiracleSpiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s. Death usually occurs within one quarter of an hour. The plant meanwhile secretes
esteraseAn esterase is a hydrolase enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis.A wide range of different esterases exist that differ in their substrate specificity, their protein structure, and their biological function.- EC classification/list...
,
peroxidasePeroxidases are a large family of enzymes that typically catalyze a reaction of the form:For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides...
,
phosphataseA phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group . This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their...
and
proteaseA protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....
enzymes. These enzymes both dissolve the insect and free the contained nutrients. The nutrient soup is then absorbed through the leaf surface and can then be used to help fuel plant growth.
All species of sundew are able to move their tentacles in response to contact with digestible prey. The tentacles are extremely sensitive and will bend toward the center of the leaf in order to bring the insect into contact with as many stalked glands as possible. According to
Charles DarwinCharles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
, the contact of the legs of a small gnat with a single tentacle is enough to induce this response. This response to touch is known as
thigmonastyThigmonasty or seismonasty is the nastic response of a plant or fungus to touch or vibration. It differs from thigmotropism in that it is independent of the direction of the stimulus. For example, tendrils from a climbing plant are thigmotropic because they twine around any support they touch. ...
, and is quite rapid in some species. The outer tentacles (recently coined as "snap-tentacles") of
D. burmanniiDrosera burmannii, the tropical sundew, is a small, compact species in the carnivorous plant genus Drosera. It normally spans only in diameter. It is one of the fastest trapping sundews as well, and its leaves can curl around an insect in only a few seconds, compared to the minutes or hours it...
and
D. sessilifoliaDrosera sessilifolia is a species in the carnivorous plant genus Drosera that is native to Brazil, Guyana, and Venezuela and grows in sandy or gravelly soils in seasonal seepages where a thin film of water collects. It produces a rosette of small, wedge-shaped to round carnivorous leaves that are...
can bend inwards toward prey in a matter of seconds after contact, while
D. glanduligeraDrosera glanduligera, the pimpernel sundew, is a rosetted annual species in the carnivorous plant genus Drosera that is endemic to Australia. It is tall and grows in most soil conditions. It produces orange flowers from August to November. It was originally described in 1844 by Johann Georg...
is known to bend these tentacles in toward prey in tenths of a second. In addition to tentacle movement, some species are able to bend their laminas to various degrees in order to maximize contact with the prey. Of these, D. capensis exhibits what is probably the most dramatic movement, curling its leaf completely around prey in 30 minutes. Some species, such as
D. filiformisDrosera filiformis, commonly known as the Thread-leaved sundew, is a small, insectivorous, rosette forming species of perennial herb. A species of sundew, it is unusual within its genus in that the long, erect, filiform leaves of this plant unroll in spirals - an arrangement similar to the...
, are unable to bend their leaves in response to prey.
A further type of (mostly strong red and yellow) emergence has recently been discovered in a few Australian species (
D. hartmeyerorumDrosera hartmeyerorum is a summer-growing annual sundew that is native to the north of Western Australia. It was discovered in 1995 by Siegfried and Irmgard Hartmeyer. Drosera hartmeyerorum has long scrambling leaves which readily curl around any unfortunate insect that lands on the leaves...
,
D. indicaDrosera indica is an insectivorous plant, a sundew native to tropical countries throughout the world, from Australia and Asia to Africa, but absent from the neotropics. Together with D. hartmeyerorum it makes up the section Arachnopus....
). Their function is not known yet, although they may help in attracting prey.
The leaf morphology of the species within the genus is extremely varied, ranging from the sessile ovate leaves of
D. erythrorhizaDrosera erythrorhiza, the red ink sundew, is a perennial tuberous species in the carnivorous plant genus Drosera that is endemic to Western Australia. It grows in a rosette and is distinguished from the other species in section Erythrorhiza by its many-flowered cymose inflorescences with up to 50...
to the bipinnately divided acicular leaves of
D. binataDrosera binata, commonly known as the Fork-leaved sundew, is a large, perennial sundew native to Australia and New Zealand. The specific epithet is Latin for "having pairs" - a reference to the leaves, which are dichotomously divided or forked...
.
Flowers and fruit
The flowers of sundews, as with nearly all carnivorous plants, are held far above the leaves by a long stem. This physical isolation of the flower from the traps was originally thought to be an adaptation meant to avoid trapping potential
pollinatorA pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain...
s; a recent study, however, indicated that Drosera attract distinct types of insects as pollinators and prey, with little overlap. Instead, the tall flower stalks probably help raise the flowers to a height where they are noticeable to pollinators. The mostly unforked
inflorescenceAn 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 are
spikesA raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
, whose flowers open one at a time and usually only remain open for a short period. Flowers open in response to light intensity (often opening only in direct sunlight), and the entire inflorescence is also
helitropicHeliotropism is the diurnal motion of plant parts in response to the direction of the sun.It is found in some members of family Malvacea e.g Malva or Lavetara...
, moving in response to the sun's position in the sky.
The radially symmetrical (actinomorphic) flowers are always perfect and have five parts (the exceptions to this rule are the four-petaled
D. pygmaeaDrosera pygmaea is a tiny, carnivorous, rosette-forming biennial or annual herb native to Australia and New Zealand. The specific epithet which translates as "dwarf" from Latin is a reference to the size of this plant which grows to between 8 and 18 mm in diameter....
and the eight to twelve-petaled
D. heterophyllaDrosera heterophylla, the swamp rainbow, is an erect perennial tuberous species in the carnivorous plant genus Drosera that is endemic to Western Australia. It grows in shallow water swamps or wet clay flats near granite outcrops and occurs in the vicinity of Perth and to its north....
). Most of the species have small flowers (<1.5 cm. or 0.6 in.). A few species, however, such as D. regia and
D. cistifloraDrosera cistiflora is a species of sundew, known for its unusually large flowers. It is native to southern Africa....
, have flowers 4 centimeters (1.5 in.) or more in diameter. In general, the flowers are white or pink. Australian species display a wider range of colors, including orange (
D. callistosDrosera callistos is a species of sundew....
), red (
D. adelaeDrosera adelae, commonly known as the lance-leaved sundew or the Adelaide sundew, is a carnivorous plant in the genus Drosera that is endemic to Queensland, Australia.-Description:...
), yellow (
D. zigzagiaDrosera zigzagia is an erect perennial tuberous species in the carnivorous plant genus Drosera. It is endemic to Western Australia and is found on the margins of salt lakes in brown sandy loam, often associated with D. salina, Stylidium insensitivum, S. pulviniforme,...
) or metallic violet colored (
D. microphyllaDrosera microphylla, the golden rainbow, is an erect perennial tuberous species in the carnivorous plant genus Drosera. It is endemic to Western Australia and grows on granite outcrops or in sandy or laterite soils. D. microphylla produces small, circular, peltate carnivorous leaves along...
).
The
ovaryIn the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the pistil which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals...
is
superiorIn the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the pistil which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals...
and develops into a dehiscent
seed capsuleIn botany a capsule is a type of simple, dry fruit produced by many species of flowering plants. A capsule is a structure composed of two or more carpels that in most cases is dehiscent, i.e. at maturity, it splits apart to release the seeds within. A few capsules are indehiscent, for example...
bearing numerous tiny seeds.
Roots
The root system of most Drosera is only weakly developed. It serves mainly to absorb water and to anchor the plant to the ground; the roots are relatively useless when it comes to nutrient uptake. A few South African species use their roots for water and food storage. Some species have wiry root systems that remain during frosts if the stem dies. Some species such as Drosera adelae and Drosera hamiltonii use their roots for asexual propagation, by sprouting plantlets along their length. Some Australian species form underground
cormA corm is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat ....
s for this purpose, which also serve to allow the plants to survive dry summers. The roots of pygmy sundews are often extremely long in proportion to their size, with a 1 centimeter (0.4 in.) plant extending roots over 15 centimeters (6 in.) beneath the soil surface. Some pygmy sundews, such as D. lasiantha and
D. scorpioidesDrosera scorpioides, commonly called the shaggy sundew, is a pygmy sundew native to the Jarrah Forest region and southern coasts of Southwest Australia. Notable for its unusually large size, D. scorpioides can produce rosettes measuring up to two inches in diameter and specimens may attain a...
, also form adventitious roots as supports. Drosera intermedia and D. rotundifolia have been reported to form
arbuscular mycorrhizaAn arbuscular mycorrhiza is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant....
s, which penetrate the plant's tissues.
Reproduction
Many species of sundews are self-fertile and flowers will often self-pollinate upon closing. Often copious amounts of seeds are produced. The tiny black seeds germinate in response to moisture and light, while seeds of temperate species also require cold, damp,
stratificationIn horticulture, stratification is the process of pretreating seeds to simulate natural winter conditions that a seed must endure before germination. Many seed species undergo an embryonic dormancy phase, and generally will not sprout until this dormancy is broken...
in order to germinate. Seeds of the tuberous species require a hot, dry summer period followed by a cool, moist winter to germinate.
Vegetative reproductionVegetative reproduction is a form of asexual reproduction in plants. It is a process by which new individuals arise without production of seeds or spores...
occurs naturally in some species that produce stolons or when roots come close to the surface of the soil. Older leaves that touch the ground may sprout plantlets. Pygmy sundews reproduce asexually using specialized scale-like leaves called
gemmaeA gemma is a single cell, or a mass of cells, or a modified bud of tissue, that detaches from the parent and develops into a new individual. This type of asexual reproduction is referred to as fragmentation. It is a means of asexual propagation in plants...
. Tuberous sundews can produce offsets from their corms.
In culture, sundews can often be propagated through leaf, crown, or root cuttings, as well as through seeds.
Distribution
The
rangeIn biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
of the sundew genus stretches from Alaska in the north to New Zealand in the south. The centers of
diversityBiodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
are Australia (with roughly 50% of all known species), South America (20+ species) and southern Africa (20+ species). A few species are also found in large parts of Eurasia and North America. These areas, however, can be considered to form the outskirts of the generic range, as the ranges of sundews do not typically approach temperated or Arctic areas. Unlike previously supposed, the evolutionary
speciationSpeciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
of this genus is no longer thought to have occurred with breakup of
GondwanaIn paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
through
continental driftContinental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...
. Rather, speciation is now thought to have occurred as a result of a subsequent wide dispersal of its range. The origins of the genus are thought to have been in Africa or Australia.
Europe is home to only three species:
D. intermediaDrosera intermedia, commonly known as the oblong-leaved sundew or spoonleaf sundew, is an insectivorous plant species belonging to the sundew genus. It is a temperate or tropical species native to Europe, southeastern Canada, the eastern half of the United States, Cuba and northern South America.-...
,
D. anglicaDrosera anglica, commonly known as the English sundew or Great sundew, is a carnivorous plant species belonging to the sundew genus. It is a temperate species with a generally circumboreal range, although it does occur as far south as Japan, southern Europe, and the island of Kauai in Hawaii, where...
, and
D. rotundifoliaDrosera rotundifolia is a species of sundew, a carnivorous plant often found in bogs, marshes and fens...
. Where the ranges of the two latter species overlap, they sometimes hybridize to form the sterile D. × obovata. In addition to the three species and the hybrid native to Europe, North America is also home to four additional species; D. brevifolia is a small
annualAn 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...
native to coastal states from
TexasTexas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
to
VirginiaThe Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, while D. capillaris, a slightly larger plant with a similar range, is also found in areas of the Caribbean. A third species,
D. linearisDrosera linearis, commonly called the slenderleaf sundew, is a sundew found in the Great Lakes region of North America, in Canada and the United States, such as in Michigan....
, is native to the northern United States and southern Canada.
D. filiformisDrosera filiformis, commonly known as the Thread-leaved sundew, is a small, insectivorous, rosette forming species of perennial herb. A species of sundew, it is unusual within its genus in that the long, erect, filiform leaves of this plant unroll in spirals - an arrangement similar to the...
has two
subspeciesSubspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
native to the East Coast of North America, the Gulf Coast, and the
Florida panhandleThe Florida Panhandle, an informal, unofficial term for the northwestern part of Florida, is a strip of land roughly 200 miles long and 50 to 100 miles wide , lying between Alabama on the north and the west, Georgia also on the north, and the Gulf of Mexico to the south. Its eastern boundary is...
.
This genus is often described as
cosmopolitanIn biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
, meaning that it has worldwide distribution. The botanist
Ludwig DielsDr. Friedrich Ludwig Emil Diels , was a German botanist.Diels was born in Hamburg, the son of the classical scholar Hermann Alexander Diels. From 1900 to 1902 he traveled together with Ernst Pritzel through South Africa, Java, Australia and New Zealand. Shortly before the first world war he...
, author of the only Monograph of the family to date, called this description an "arrant misjudgment of this genus' highly unusual distributional circumstances" („arge Verkennung ihrer höchst eigentümlichen Verbreitungsverhältnisse“), while admitting that sundew species do "occupy a significant part of the Earth's surface" („einen beträchtlichen Teil der Erdoberfläche besetzt“). He particularly pointed to the absence of Drosera species from almost all
aridA region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...
climate zones, countless
rainforestRainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
s, the American Pacific Coast,
PolynesiaPolynesia is a subregion of Oceania, made up of over 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are termed Polynesians and they share many similar traits including language, culture and beliefs...
, the Mediterranean region, and North Africa, as well as the scarcity of species diversity in temperate zones such as Europe and North America.
Habitat
Sundews generally grow in seasonally moist or more rarely constantly wet habitats with acidic soils and high levels of sunlight. Common habitats include
bogA bog, quagmire or mire is a wetland that accumulates acidic peat, a deposit of dead plant material—often mosses or, in Arctic climates, lichens....
s,
fenA fen is a type of wetland fed by mineral-rich surface water or groundwater. Fens are characterised by their water chemistry, which is neutral or alkaline, with relatively high dissolved mineral levels but few other plant nutrients...
s,
swampA swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
s,
marshIn geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
es, the
tepuiA tepui , or tepuy, is a table-top mountain or mesa found in the Guiana Highlands of South America, especially in Venezuela. The word tepui means "house of the gods" in the native tongue of the Pemon, the indigenous people who inhabit the Gran Sabana....
s of Venezuela, the
wallumWallum, or Wallum country, is an Australian ecosystem of coastal south-east Queensland, extending into north-eastern New South Wales. It is characterised by floristically-rich shrubland and heathland on deep, nutrient-poor acidic sandy soils and regular wildfire. Seasonal changes in the...
s of coastal Australia, the
FynbosFynbos is the natural shrubland or heathland vegetation occurring in a small belt of the Western Cape of South Africa, mainly in winter rainfall coastal and mountainous areas with a Mediterranean climate...
of South Africa, and moist streambanks. Many species grow in association with sphagnum moss, which absorbs much of the soil's nutrient supply and also acidifies the soil, making nutrients less available to plant life. This allows sundews, which don't rely on soil-bound nutrients, to flourish where more dominating vegetation would usually outcompete them.
That being said, the genus is very variable in terms of habitat. Individual sundew species have adapted to a wide variety of environments, including atypical habitats such as rainforests, deserts (ex.
D. burmanniiDrosera burmannii, the tropical sundew, is a small, compact species in the carnivorous plant genus Drosera. It normally spans only in diameter. It is one of the fastest trapping sundews as well, and its leaves can curl around an insect in only a few seconds, compared to the minutes or hours it...
and
D. indicaDrosera indica is an insectivorous plant, a sundew native to tropical countries throughout the world, from Australia and Asia to Africa, but absent from the neotropics. Together with D. hartmeyerorum it makes up the section Arachnopus....
), and even highly shaded environments (Queensland Sundews). The temperate species, which form
hibernaculaHibernaculum is the term often applied to a winter bud of certain aquatic plants, such as the bladderworts . The buds are heavier than water, and, being developed at the approach of cold weather, they become detached, sink to the bottom of the pond, and thus survive the winter...
in the winter, are an example of such adaptation to habitats; in general, sundews tend to prefer warm climates, and are only moderately frost-resistant.
Conservation status
Although none of the Drosera species in the United States are federally protected, all are listed as
threatenedThreatened species are any speciesg animals, plants, fungi, etc.) which are vulnerable to endangerment in the near future.The World Conservation Union is the foremost authority on threatened species, and treats threatened species not as a single category, but as a group of three categories,...
or
endangeredAn endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
in some states. Additionally, many of the remaining native populations lie on protected land such as
National ParkA national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual nations designate their own national parks differently A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or...
s or Wildlife Preserves. Drosera species are protected by law in many European countries, such as Germany, Austria, Switzerland, Czech republic, Finland,
HungaryHungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
,
FranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, and Bulgaria. Currently, the largest threat in Europe and North America is that of habitat destruction for development projects, as well as the draining of bogs for agricultural uses and peat harvesting. In many regions this has led to the extinction of some species from parts of their former range. Re-introduction of plants into such habitats is usually difficult or impossible, as the ecological needs of certain population is closely tied to their geographical location. Through increased legal protection of bogs and moors as well as a concentrated effort to renaturalize such habitats, the threat to these plant's survival might be curbed, although most species would remain endangered. The relatively unimpressive image of these plant as well as their small, low growth makes them difficult to protect. As part of the landscape, sundews are often overlooked or not recognized at all.
In South Africa and Australia, two of the three centers of
species diversitySpecies diversity is an index that incorporates the number of species in an area and also their relative abundance. It is a more comprehensive value than species richness....
, the natural habitats of these plants are undergoing a high degree of pressure from human activities. Expanding population centers (such as
QueenslandQueensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
,
PerthPerth is the capital and largest city of the Australian state of Western Australia and the fourth most populous city in Australia. The Perth metropolitan area has an estimated population of almost 1,700,000....
, and
Cape TownCape Town is the second-most populous city in South Africa, and the provincial capital and primate city of the Western Cape. As the seat of the National Parliament, it is also the legislative capital of the country. It forms part of the City of Cape Town metropolitan municipality...
) threaten many such habitats, as does the draining of moist areas for agriculture and forestry in rural areas. The droughts that have been sweeping Australia over the last ten years also pose a threat to many species by drying up previously moist areas.
Those species that are endemic to a very limited area are often most threatened by the collection of plants from the wild.
D. madagascariensisDrosera madagascariensis is a carnivorous plant of the Sundew genus . It was described in 1824 by A. P. de Candolle and is native to Africa.-Description:...
is considered endangered in
MadagascarThe Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
because of the largescale removal of plants from the wild for exportation; 10 - 200 million plants are harvested for commercial medicinal use annually.
Uses
As a medicinal plant
Several medicinally active compounds are found in sundews, including
flavonoidFlavonoids , are a class of plant secondary metabolites....
s (
kaempferolKaempferol is a natural flavonol, a type of flavonoid, that has been isolated from tea, broccoli, Delphinium, Witch-hazel, grapefruit,cabbage, kale, beans, endive, leek, tomato, strawberries, grapes, brussels sprouts, apples and other plant sources. Kaempferol is a yellow crystalline solid with a...
,
myricetinMyricetin is a naturally occurring flavonol, a flavonoid found in many grapes, berries, fruits, vegetables, herbs, as well as other plants. Walnuts are a rich dietary source. Trace amounts can be found as glycosides. It is one of the phenolic compounds present in red wine.Myricetin has antioxidant...
,
quercetinQuercetin , a flavonol, is a plant-derived flavonoid found in fruits, vegetables, leaves and grains. It also may be used as an ingredient in supplements, beverages or foods.-Occurrence:...
and
hyperosideHyperoside is a chemical compound. It is the 3-O-galactoside of quercetin. It is a medicinally active compound that can be isolated from Drosera rotundifolia, from the Stachys plant, from Prunella vulgaris, from Rumex acetosella, Cuscuta Chinensis seeds and from St John's wort.In Rheum nobile and R...
), quinones (plumbagin, hydroplumbagin glucoside and rossoliside (7 – methyl – hydrojuglone – 4 – glucoside)), and other constituents such as
carotenoidCarotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s, plant acids (e.g.
butyric acidButyric acid , also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula CH3CH2CH2-COOH. Salts and esters of butyric acid are known as butyrates or butanoates...
,
citric acidCitric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
,
formic acidFormic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
,
gallic acidGallic acid is a trihydroxybenzoic acid, a type of phenolic acid, a type of organic acid, also known as 3,4,5-trihydroxybenzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H23COOH. Gallic acid is found both free and as part of...
,
malic acidMalic acid is an organic compound with the formula HO2CCH2CHOHCO2H. It is a dicarboxylic acid which is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms , though only the L-isomer exists...
,
propionic acidPropanoic acid is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent odor...
),
resinResin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
, tannins and
ascorbic acidAscorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form of vitamin C. The name is derived from a- and scorbutus , the...
(vitamin C).
Sundews were used as medicinal herbs as early as the 12th century, when an Italian doctor from the School of Salerno by the name of Matthaeus Platearius described the plant as an herbal remedy for
coughA cough is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes...
s under the name "herba sole". It has been used commonly in cough preparations in Germany and elsewhere in Europe. Sundew tea was especially recommended by herbalists for dry coughs,
bronchitisAcute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...
, whooping cough,
asthmaAsthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
and "bronchial cramps". A modern study has shown that Drosera does exhibit antitussive properties.
Culbreth's 1927 Materia Medica listed
D. rotundifoliaDrosera rotundifolia is a species of sundew, a carnivorous plant often found in bogs, marshes and fens...
,
D. anglicaDrosera anglica, commonly known as the English sundew or Great sundew, is a carnivorous plant species belonging to the sundew genus. It is a temperate species with a generally circumboreal range, although it does occur as far south as Japan, southern Europe, and the island of Kauai in Hawaii, where...
and
D.linearisDrosera linearis, commonly called the slenderleaf sundew, is a sundew found in the Great Lakes region of North America, in Canada and the United States, such as in Michigan....
as being used as stimulants and expectorants, and "of doubtful efficacy" for treating
bronchitisAcute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...
, whooping cough, and
tuberculosisTuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
. Sundews have also been used as an
aphrodisiacAn aphrodisiac is a substance that increases sexual desire. The name comes from Aphrodite, the Greek goddess of sexuality and love. Throughout history, many foods, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable...
and to strengthen the heart, as well as to treat sunburn, toothache, and prevent freckles. They are still used today in some 200-300 registered medications, usually in combination with other active ingredients. Today Drosera is usually used to treat ailments such as
asthmaAsthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, coughs, lung infections, and stomach ulcers.
Medicinal preparations are primarily made using the roots, flowers, and fruit-like capsules. Since all native sundews species are protected in many parts of Europe and North America, extracts are usually prepared using cultivated fast-growing sundews (specifically
D. rotundifoliaDrosera rotundifolia is a species of sundew, a carnivorous plant often found in bogs, marshes and fens...
,
D. intermediaDrosera intermedia, commonly known as the oblong-leaved sundew or spoonleaf sundew, is an insectivorous plant species belonging to the sundew genus. It is a temperate or tropical species native to Europe, southeastern Canada, the eastern half of the United States, Cuba and northern South America.-...
,
D. anglicaDrosera anglica, commonly known as the English sundew or Great sundew, is a carnivorous plant species belonging to the sundew genus. It is a temperate species with a generally circumboreal range, although it does occur as far south as Japan, southern Europe, and the island of Kauai in Hawaii, where...
, D. ramentacea and
D. madagascariensisDrosera madagascariensis is a carnivorous plant of the Sundew genus . It was described in 1824 by A. P. de Candolle and is native to Africa.-Description:...
) or from plants collected and imported from Madagascar, Spain, France, Finland and the Baltics.
As ornamental plants
Because of their carnivorous nature and the beauty of their glistening traps, sundews have become favorite
ornamental plantOrnamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
s - however, the environmental requirements of most species are relatively stringent and can be difficult to meet in cultivation. As a result, most species are unavailable commercially. A few of the hardiest varieties, however, have made their way into the mainstream nursery business and can often be found for sale next to
Venus flytrapThe 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. These most often include D. capensis, D. aliciae, and
D. spatulataDrosera spatulata, the spoon-leaved sundew, is a variable, rosette-forming sundew with spoon-shaped leaves. The specific epithet is Latin for "spatula shaped," a reference to the form of the leaves...
.
Cultivation requirements vary greatly by species. In general, however, sundews require a high environmental moisture content, usually in the form of a constantly moist or wet soil substrate. Most species also require this water to be pure, as nutrients, salts, or minerals in their soil can stunt their growth or even kill them. Commonly plants are grown in a soil substrate containing some combination of dead or live sphagnum moss,
sphagnumSphagnum is a genus of between 151 and 350 species of mosses commonly called peat moss, due to its prevalence in peat bogs and mires. A distinction is made between sphagnum moss, the live moss growing on top of a peat bog on one hand, and sphagnum peat moss or sphagnum peat on the other, the...
peat moss, sand, and/or
perlitePerlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently...
, and are watered with
distilledDistilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.-History:...
,
ROReverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
, or rain water.
Other uses
The
cormA corm is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat ....
s of the tuberous sundews native to Australia are considered a delicacy by the
Australian AboriginesAustralian Aborigines , also called Aboriginal Australians, from the latin ab originem , are people who are indigenous to most of the Australian continentthat is, to mainland Australia and the island of Tasmania...
. Some of these corms were also used to dye textiles, while another purple or yellow dye was
traditionally preparedTraditional dyes of the Scottish Highlands are thenative vegetable dyes used in Scottish Gaeldom.The following are the principal dyestuffs with the colours they produce. Several of the tints are very bright, but have now been superseded by various mineral dyes. The Latin names are given where known...
in the
Scottish HighlandsThe Highlands is an historic region of Scotland. The area is sometimes referred to as the "Scottish Highlands". It was culturally distinguishable from the Lowlands from the later Middle Ages into the modern period, when Lowland Scots replaced Scottish Gaelic throughout most of the Lowlands...
using
D. rotundifoliaDrosera rotundifolia is a species of sundew, a carnivorous plant often found in bogs, marshes and fens...
. A sundew
liqueurA liqueur is an alcoholic beverage that has been flavored with fruit, herbs, nuts, spices, flowers, or cream and bottled with added sugar. Liqueurs are typically quite sweet; they are usually not aged for long but may have resting periods during their production to allow flavors to marry.The...
is also still produced using a recipe that has its roots in the 14th century. It is made using fresh leaves from mainly D. capensis,
D. spatulataDrosera spatulata, the spoon-leaved sundew, is a variable, rosette-forming sundew with spoon-shaped leaves. The specific epithet is Latin for "spatula shaped," a reference to the form of the leaves...
, and D. rotundifolia.
Phylogenetics
- For a complete list of species, see the separate article List of Drosera species.
The unrooted
cladogramA 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...
to the right shows the relationship between various subgenera and classes as defined by the Rivadavia et al.s analysis in 2002. The monotypic section Meristocaulis was not included in the study, so that its place in this system is unclear. More recent studies have placed this group near section Bryastrum, so it is placed there below. It should also be noted that the placement of the section Regiae in relation to Aldrovanda and Dionaea is uncertain. Since the section Drosera is polyphyletic, it shows up multiple times in the cladogram (*).
This phylogenetic study has made the need for a revision of the genus even clearer.
Sources
Much of the content of this article comes from the equivalent German-language wikipedia article (retrieved April 30, 2006).
- Barthlott, Wilhelm; Porembski, Stefan; Seine, Rüdiger; Theisen, Inge: Karnivoren. Stuttgart, 2004, ISBN 3-8001-4144-2
- Correa A., Mireya D.; Silva, Tania Regina Dos Santos: Drosera (Droseraceae), in: Flora Neotropica, Monograph 96, New York, 2005
- Darwin, Charles: Insectivorous Plants, 1875
- Lowrie, Allen: Carnivorous Plants of Australia, Vol. 1-3, English, Nedlands, Western Australia, 1987–1998
- Lowrie, Allen: A taxonomic revision of Drosera section Stolonifera (Droseraceae) from south-west Western Australia, 2005, Nuytsia 15(3):355-393. (Online: http://science.calm.wa.gov.au/nuytsia/15/3/355-394.pdf)
- Olberg, Günter: Sonnentau, Natur und Volk, Bd. 78, Heft 1/3, pp. 32–37, Frankfurt, 1948
- Rivadavia, Fernando; Kondo, Katsuhiko; Kato, Masahiro und Hasebe, Mitsuyasu: Phylogeny of the sundews, Drosera (Droseraceae), based on chloroplast rbcL and nuclear 18S ribosomal DNA Sequences, American Journal of Botany. 2003;90:123-130. (Online: http://www.amjbot.org/cgi/content/full/90/1/123)
- Seine, Rüdiger; Barthlott, Wilhelm: Some proposals on the infrageneric classification of Drosera L., Taxon 43, 583 - 589, 1994
- Schlauer, Jan: A dichotomous key to the genus Drosera L. (Droseraceae), Carnivorous Plant Newsletter, Vol. 25 (1996)
External links