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Sundew

2007 Schools Wikipedia Selection. Related subjects: Plants

                  iDrosera
   Drosera spatulata Kansai
   Drosera spatulata Kansai
         Scientific classification

   Kingdom:  Plantae
   Division: Magnoliophyta
   Class:    Magnoliopsida
   Order:    Caryophyllales
   Family:   Droseraceae
   Genus:    Drosera
             L.

                                   Species

   See separate list.

   The Sundews (Drosera) comprise one of the largest genera of carnivorous
   plants, with over 170 species. These members of the family Droseraceae
   lure, capture, and digest insects using stalked mucilaginous glands
   covering their leaf surface. The insects are used to supplement the
   poor mineral nutrition that sundews are able to obtain from the soil
   they grow in. 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 Greek δρόσος: "drosos" = "dew,
   dewdrops") as well as the English common name (sundew) refer to the
   glistening drops of mucilage at the tip of each tentacle that resemble
   drops of morning dew.

Plant characteristics

   Sundews are perennial (or rarely annual) herbacious (non-woody) plants,
   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. erythrogyna. Sundews have been
   shown to be able to achieve a lifespan of 50 years. The genus is so
   specialized for nutrient uptake through its carnivory that in at least
   the case of pygmy sundews it is missing the enzymes ( nitrate reductase
   in particular ) that plants usually 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 in a winter dormancy period (=
       Hemicryptophyte). All of the North American and European species
       belong to this group.Drosera arcturi from the mountains of New
       Zealand is another temperate species that dies back to thick, wiry
       roots.
     * Subtropical Sundews: These species maintain vegetative growth
       year-round under uniform or nearly uniform climatic conditions.

   A tuber of D. zonaria, a tuberous sundew, beginning its winter growth
   Enlarge
   A tuber of D. zonaria, a tuberous sundew, beginning its winter growth
     * Pygmy Sundews: A group of roughly 40 Australian species, they are
       distinguished by miniature growth, the formation of gemmae for
       asexual reproduction, and dense formation of hairs in the crown
       centre. These hairs serve to protect the plants from Australia's
       intense summer sun. Pygmy sundews form the section Bryastrum.
     * Tuberous Sundews: More than 40 Australian species that form an
       underground corm in order to survive the extremely dry summers of
       their habitat, re-emerging in the fall. 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 Ergaleium.

   D. derbyensis, from the petiolaris complex
   Enlarge
   D. derbyensis, from the petiolaris complex
     * 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 petioles densely covered in trichomes,
       which maintain a sufficiently humid environment and serve as an
       increased condensation surface for morning dew. The petiolaris
       complex sundews comprise the section Lasiocephala.

   Although they do not form a single strictly defined growthform, a
   number of species are often put together in a further group:
     * Queensland Sundews: A small group of three species ( D. schizandra,
       D. prolifera, and D. adelae), all native to highly humid habitats
       in the dim understories of the Australian rainforest.

Leaves and carnivory

   Leaf and tentacle movement on D. capensis
   Enlarge
   Leaf and tentacle movement on D. capensis

   Sundews are characterised by the glandular tentacles, topped with
   sticky secretions, that cover their laminae. 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 sessile glands that absorb the resulting nutrient soup
   (the latter glands are missing in some species, such as D.
   erythrorhiza). Small prey, mainly consisting of insects, are attracted
   by the sweet secretions of the peduncular glands. Upon touching these,
   however, they 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 spiracles. Death usually occurs within one quarter
   of an hour. The plant meanwhile secretes esterase, peroxidase,
   phosphatase and protease 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.
   Drosera spathulata with a captured fly
   Enlarge
   Drosera spathulata with a captured fly

   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 centre of the leaf in order to bring the insect
   into contact with as many stalked glands as possible. According to
   Charles Darwin, 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 thigmotropism, and is quite rapid in some species. The outer
   tentacles (recently coined as "snap-tentacles") of D. burmannii and D.
   sessilifolia can bend inwards toward prey in a matter of seconds after
   contact, while D. glanduligera is known to bend these tentacles in
   toward prey in mere 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 12-72 hours. Some species, such as
   D. filiformis, are unable to bend their leaves in response to prey.

   The leaf morphology of the species within the genus is extremely
   varied, ranging from the sessile ovate leaves of D. erythrorhiza to the
   bipinnately divided acicular leaves of D. binata.

Flowers and fruit

   Flower of D. kenneallyi
   Enlarge
   Flower of D. kenneallyi

   The flowers of sundews, as with nearly all carnivorous plants, are held
   far above the leaves by a long stem in order to avoid trapping
   potential pollinators. The mostly unforked inflorescences are spikes,
   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
   helitropic, 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. pygmaea and the eight to twelve-petaled D. heterophylla). Most of
   the species have small flowers (<1.5 cm. or 0.6 in.). A few species,
   however, such as D. regia and D. cistiflora, 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. callistos), red ( D. adelae), yellow ( D. zigzagia) or
   metallic violet colored ( D. microphylla).

   The ovary is superior and develops into a dehiscent seed capsule
   bearing numerous tiny seeds.

Roots

   The root system of most Drosera is only weakly developed. It serves
   mainly to absorb water to and 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 thier
   length. Some Australian species form underground corms 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. scorpiodes, also form adventitious roots as
   supports.

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,
   stratification in order to germinate. Seeds of the tuberous species
   require a hot, dry summer period followed by a cool, moist winter to
   germinate.

   Vegetative reproduction 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 gemmae.
   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

   Distribution of the genus Drosera
   Enlarge
   Distribution of the genus Drosera

   The range of the sundew genus stretches from Alaska in the north to New
   Zealand in the south. The centers of diversity 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 speciation of this genus is no
   longer thought to have occurred with break-up of Gondwana through
   continental drift. 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.
   Drosera filiormis filiformis in a peat bog in New Jersey
   Enlarge
   Drosera filiormis filiformis in a peat bog in New Jersey

   Europe is home to only three species: D. intermedia, D. anglica, and D.
   rotundifolia. 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 annual
   native to coastal states from Texas to Virginia, while D. capillaris, a
   slightly larger plant with a similar range, is also found in areas of
   the Caribbean. A third species, D. linearis, is native to the northern
   United States and southern Canada. D. filiformis has two subspecies
   native to the East Coast, the Gulf Coast, and the Florida panhandle.

   This genus is often descriped as cosmopolitan, meaning that it has
   worldwide distribution. The botanist Ludwig Diels, 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 arid climate
   zones, countless rainforests, the American Pacific Coast, Polynesia,
   the Mediterranean, and North Africa, as well as the scarcity of species
   diversity in temperate zones such as Europe and North America.

Habitat

   Round-leaf sundew (D. rotundifolia) growing in sphagnum moss along with
   sedges and Equisetum in Mt. Hood National Forest, Oregon
   Enlarge
   Round-leaf sundew ( D. rotundifolia) growing in sphagnum moss along
   with sedges and Equisetum in Mt. Hood National Forest, Oregon

   Sundews generally grow in seasonally moist or more rarely constantly
   wet habitats with acidic soils and high levels of sunlight. Common
   habitats include bogs, fens, swamps, marshes, the tepuis of Venezuela,
   the wallums of coastal Australia, the Fynbos 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. burmannii and D. indica), and even highly shaded environments
   (Queensland Sundews). The temperate species, which form hibernacula 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 threatened or endangered in some states.
   Additionally, many of the remaining native populations lie on protected
   land such as National Parks or Wildlife Preserves. Drosera species are
   protected by law in many European countries, such as Germany, Austria,
   Switzerland, Czech republic, Finland, Hungary, 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 special
   diversity, the natural habitats of these plants are undergoing a high
   degree of pressure from human activities. Expanding population centers
   (such as Queensland, Perth, and Cape Town) 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, which likely are a result of global warming, 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.
   madagascariensis is considered endangered in Madagascar because of the
   largescale removal of plants from the wild for exportation; 10 - 200
   million plants are harvested for commercial medicinal use annually.

Uses

   Possibly the oldest illustration of a sundew from the mysterious
   Voynich manuscript
   Enlarge
   Possibly the oldest illustration of a sundew from the mysterious
   Voynich manuscript

As a medicinal plant

   Several medicinally active compounds are found in sundews, including
   flavinoids ( kaempferol, myricetin, quercetin and hyperoside), quinones
   (plumbagin, hydroplumbagin glucoside and rossoliside
   (7–methyl–hydrojuglone–4–glucoside)), and other constituents such as
   carotenoids, plant acids (e.g. butyric acid, citric acid, formic acid,
   gallic acid, malic acid, propionic acid), resin, tannins and ascorbic
   acid (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 coughs under the
   name "herba sole". It has been used commonly in cough preparations in
   Germany and elswhere in Europe. Sundew tea was especially recommended
   by herbalists for dry coughs, bronchitis, whooping cough, asthma and
   "bronchial cramps". A modern study has shown that Drosera does exhibit
   antitussive properties. Sundews have also been used as an aphrodisiac
   and to strengthen the heart, as well as to treat sunburn 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 asthma, 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. rotundifolia, D.
   intermedia, D. anglica, D. ramentacea and D. madagascariensis) 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 plants. The
   environmental needs of most species are relatively stringent and can be
   difficult to maintain. 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 fly traps. These most often include D. capensis, D.
   aliciae, and D. spatulata.

   The more difficult species of sundews are also cultivated by a group of
   several thousand carnivorous plant enthusiasts world wide; virtually
   every species can be found in cultivation. Since many sundew species
   are only found in small numbers in a very limited range in the wild,
   several species have been threatened by aggressive collection of plant
   material for cultivation.

   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 or kill them. Commonly plants are grown in a soil
   substrate containing some combination of dead or live sphagnum moss,
   sphagnum peat moss, sand, and/or perlite, and are watered with
   distilled, RO, or rain water.

Other uses

   The corms of the tuberous sundews native to Australia are considered a
   delicacy by the Australian Aborigines. Some of these corms were also
   used to dye textiles, while another purple or yellow die was
   traditionally prepared in the Scottish Highlands using D. rotundifolia.
   A sundew liqueur 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. spatulata, and D. rotundifolia.

Phylogenetics

   The following cladogram shows the relationship between various
   subgenera and classes as defined by the Rivadavia et al.'s analysis in
   2002. The monotypic section "Meristocaules" 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. 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.






   Section Drosera*

   Section Ptycnostigma

   Section Drosera*

   Section Thelocalyx


   Subgenus Ergaleium

   Subgenus Phycopsis


   Section Bryastrum

   Section Lasiocephala

   Section Coelophylla

   Section Drosera: Drosera arcturi*

   Section Regiae

   Aldovandra

   Dionaea

   Retrieved from " http://en.wikipedia.org/wiki/Sundew"
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   with only minor checks and changes (see www.wikipedia.org for details
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