Drosera, commonly known as the sundews, is one of the largest genera
of carnivorous plants, with at least 194 species. These members of
Droseraceae lure, capture, and digest insects using stalked
mucilaginous glands covering their leaf surfaces. The insects are used
to supplement the poor mineral nutrition of the soil in which the
plants grow. Various species, which vary greatly in size and form, are
native to every continent except Antarctica.
Both the botanical name (from the Greek δρόσος: drosos = "dew,
dewdrops") and the English common name (sundew, derived from
solis, meaning "dew of the sun") refer to the glistening drops of
mucilage at the tip of each tentacle that resemble drops of morning
1.2 Leaves and carnivory
1.3 Flowers and fruit
2 Taxonomy and phylogenetics
6 Conservation status
7.1 As a medicinal plant
7.2 As ornamental plants
7.4 Other uses
8 Chemical constituents
11 External links
A tuber of D. zonaria, a tuberous sundew, beginning its winter growth
Sundews are perennial (or rarely annual) herbaceous plants, forming
prostrate or upright rosettes between 1 and 100 cm (0.39 and
39.37 in) in height, depending on the species. Climbing species
form scrambling stems which can reach much longer lengths, up to
3 m (9.8 ft) in the case of D. erythrogyne. Sundews
have been shown to be able to achieve a lifespan of 50 years. The
genus is specialized for nutrient uptake through its carnivorous
behavior, for example the pygmy sundew is missing the enzymes (nitrate
reductase, in particular) that plants normally use for the uptake
of earth-bound nitrates.
The genus can be divided into several habits, or 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 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 for asexual
reproduction, 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: These nearly 50 Australian species form an
underground tuber 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 Ergaleium.
D. derbyensis, from the petiolaris complex
Petiolaris complex: A group of tropical Australian species, they live
in constantly warm but sometimes 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 comprises the subgenus
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,
D. schizandra and D. prolifera), all are native to highly
humid habitats in the dim understories of the Australian rainforest.
Leaves and carnivory
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, 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 spiracles. Death usually occurs within
15 minutes. The plant meanwhile secretes esterase, peroxidase,
phosphatase and protease enzymes. These enzymes dissolve the insect
and free the nutrients contained within it. This nutrient mixture is
then absorbed through the leaf surfaces to be used by the rest of the
Drosera Glandular Hair
All species of sundew are able to move their tentacles in response to
contact with edible prey. The tentacles are extremely sensitive and
will bend toward the center of the leaf 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 thigmonasty, 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 tenths of a second. In addition
to tentacle movement, some species are able to bend their laminae to
various degrees 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. filiformis, are unable to bend their leaves in
response to prey.
Emergences of an Australian D. indica
A further type of (mostly strong red and yellow) emergence has
recently been discovered in a few Australian species (D.
hartmeyerorum, D. indica). 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. erythrorhiza to
the bipinnately divided acicular leaves of D. binata.
Flowers and fruit
Flower of D. kenneallyi
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 is commonly thought to be an adaptation
meant 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 12-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 cm (1.6 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 (D. microphylla).
The ovary is superior and develops into a dehiscent seed capsule
bearing numerous tiny seeds. The pollen grain type is compound, which
means four microspores (pollen grains) are stuck together with a
protein called callose.
Drosera anglica with prey
The root systems of most
Drosera are often only weakly developed.
Serving mainly to absorb water and to anchor the plant to the ground,
the roots are relatively useless for 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 D. adelae and D. hamiltonii, use their
roots for asexual propagation, by sprouting plantlets along their
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-cm (0.4-in) plant extending roots over 15 cm
(5.9 in) beneath the soil surface. Some pygmy sundews, such as D.
lasiantha and D. scorpioides, also form adventitious roots as
supports. D. intermedia and D. rotundifolia have been reported to form
arbuscular mycorrhizae, which penetrate the plant's tissues.
Taxonomy and phylogenetics
Taxonomy of Drosera
Taxonomy of Drosera and List of
The unrooted cladogram to the right shows the relationship between
various subgenera and classes as defined by the analysis of Rivadavia
et al. in 2002. The monotypic section Meristocaulis was not
included in the study, so its place in this system is unclear. More
recent studies have placed this group near section Bryastrum, so it is
placed there below. Also of note, the placement of the section Regiae
in relation to
Aldrovanda and Dionaea is uncertain. Since the
Drosera is polyphyletic, it shows up multiple times in the
This phylogenetic study has made the need for a revision of the genus
Many species of sundews are self-fertile; their flowers will often
self-pollinate upon closing. Often, numerous seeds are produced.
The tiny black seeds germinate in response to moisture and light,
while seeds of temperate species also require cold, damp,
stratification 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.
See also: Carnivorous plants of Australia
Distribution of the genus
Drosera shown in green
Drosera filiformis var. filiformis in a peat bog in New Jersey
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, and South America and southern
Africa, each with more than 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 temperate or Arctic areas.
Contrary to previous supposition, the evolutionary speciation of this
genus is no longer thought to have occurred with the breakup 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
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. The third species, D. linearis, is
native to the northern United States and southern Canada. D.
filiformis has two subspecies native to the East Coast of North
America, the Gulf Coast, and the Florida panhandle.
This genus is often described as cosmopolitan, meaning 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 sundew species do "occupy
a significant part of the Earth's surface (einen beträchtlichen Teil
der Erdoberfläche besetzt)". He particularly pointed to the
Drosera species from almost all arid climate zones,
countless rainforests, the American Pacific Coast, Polynesia, the
Mediterranean region, and North Africa, as well as the scarcity of
species diversity in temperate zones, such as Europe and North
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 do not rely on soil-bound nutrients, to
flourish where more dominating vegetation would usually outcompete
The genus, though, 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 (D.
burmannii and D. indica), and even highly shaded environments
Queensland sundews). The temperate species, which form hibernacula in
the winter, are examples of such adaptation to habitats; in general,
sundews tend to inhabit warm climates, and are only moderately
Leaf of the common sundew,
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
Drosera species are protected by law in many European
countries, such as Germany, Austria, Switzerland, the Czech
Republic, Finland, Hungary, France, and Bulgaria.
Currently, the largest threat in Europe and North America is 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 extirpation of some species from parts of their former
range. Reintroduction of plants into such habitats is usually
difficult or impossible, as the ecological needs of certain
populations 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
plants' survival might be curbed, although most species would remain
endangered. The relatively unimpressive image of these plants, as well
as their small, low growth, makes them difficult to protect.[citation
needed] 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
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 10 years also pose a threat to many species by
drying up previously moist areas.
Those species 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 large-scale removal
of plants from the wild for exportation; 10 - 200 million plants are
harvested for commercial medicinal use annually.
This page of the 15th century
Voynich manuscript might possibly show
one of the oldest illustrations of a
Drosera species
As a medicinal plant
Sundews were used as medicinal herbs as early as the 12th century,
when an Italian doctor from the School of Salerno, 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 elsewhere 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 exhibits antitussive properties.
Culbreth's 1927 Materia Medica listed D. rotundifolia, D. anglica and
D.linearis as being used as stimulants and expectorants, and "of
doubtful efficacy" for treating bronchitis, whooping cough, and
tuberculosis. Sundews have also been used as an aphrodisiac and to
strengthen the heart, as well as to treat sunburn, toothache, and
prevent freckles.[dubious – discuss] They are still used today in
some 200-300 registered medications, usually in combination with other
herbal ingredients. Today,
Drosera is usually used to
treat ailments such as asthma, coughs, lung infections, and stomach
ulcers.[medical citation needed]
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; 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 flytraps. These most often
include D. capensis, D. aliciae, and D. spatulata.
Cultivation requirements vary greatly by species. In general, though,
sundews require 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, sphagnum peat moss, sand, and/or perlite, and are
watered with distilled, reverse osmosis, or rain water.
The mucilage produced by
Drosera has remarkable elastic properties and
has made this genus a very attractive subject in biomaterials
research. In one recent study, the adhesive mucilages of three species
(D. binata, D. capensis, and D. spatulata) were
analyzed for nanofiber and nanoparticle content. Using atomic
force microscopy, transmission electron microscopy, and
energy-dispersive X-ray spectroscopy, researchers were able to observe
networks of nanofibers and nanoparticles of various sizes within the
mucilage residues. In addition, calcium, magnesium, and chlorine –
key components of biological salts - were identified. These
nanoparticles are theorized to increase the viscosity and stickiness
of the mucilage, in turn increasing the effectiveness of the trap.
More importantly for biomaterials research, however, is the fact that,
when dried, the mucin provides a suitable substrate for the attachment
of living cells. This has important implications for tissue
engineering, especially because of the elastic qualities of the
adhesive. Essentially, a coating of
Drosera mucilage on a surgical
implant, such as a replacement hip or an organ transplant, could
drastically improve the rate of recovery and decrease the potential
for rejection, because living tissue can effectively attach and grow
on it. The authors also suggest a wide variety of applications for
Drosera mucin, including wound treatment, regenerative medicine, or
enhancing synthetic adhesives. Also of note, because this mucilage
can stretch to nearly a million times its original size and is readily
available for use, it can be an extremely cost-efficient source of
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 dye was
traditionally prepared in the
Scottish Highlands using D.
rotundifolia. A sundew liqueur is also still produced using a
recipe from the 14th century. It is made using fresh leaves from
mainly D. capensis, D. spatulata, and D. rotundifolia.
Several chemical compounds with potential biological activities are
found in sundews, including flavonoids (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).
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Plant Newsletter, Vol. 25 (1996)
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