Drosera

Drosera
Drosera tokaiensis
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Order:	Caryophyllales
Family:	Droseraceae
Genus:	Drosera L.
Subgenera
Acturia Bryastrum Coelophylla Drosera Ergaleium Lasiocephala Meristocaulis Phycopsis Regiae Stelogyne Thelocalyx
Synonyms[1]
Adenopa Raf. Dismophyla Raf. Drossera Gled. Esera Neck. Filicirna Raf. Freatulina Chrtek & Slavíková Rorella Hill Rossolis Adans. Sondera Lehm.

Drosera, which is commonly known as the sundews, is one of the largest genera of carnivorous plants, with at least 194 species.^[2] These members of the family Droseraceae^[1] 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.^[3]

Charles Darwin performed much of the early research into Drosera, engaging in a long series of experiments with Drosera rotundifolia which were the first to confirm carnivory in plants.^[4][5][6] In an 1860 letter, Darwin wrote, “…at the present moment, I care more about Drosera than the origin of all the species in the world.”^[7]

Taxonomy

The botanical name from the Greek δρόσος drosos "dew, dewdrops"^[8] refer to the glistening drops of mucilage at the tip of the glandular trichomes that resemble drops of morning dew. The English common name sundew also describes this, derived from Latin ros solis meaning "dew of the sun".

The Principia Botanica, published in 1787, states “Sun-dew (Drosera) derives its name from small drops of a liquor-like dew, hanging on its fringed leaves, and continuing in the hottest part of the day, exposed to the sun.”^[9]

Phylogenetics

The unrooted

This phylogenetic study has made the need for a revision of the genus even clearer.

Description

Sundews are

The genus can be divided into several habits, or growth forms:

• Temperate sundews: These species form a tight cluster of unfurled leaves called a
  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.

• 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 Lasiocephala.

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

Sundews are characterised by the glandular tentacles, topped with sticky secretions, that cover their

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.^[6] 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.^[14] In addition to tentacle movement, some species are able to bend their leaves 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.^[15]

A further type of (mostly strong red and yellow) leaf coloration 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.

While the exact physiological mechanism of the sundew's carnivorous response is not yet known, some studies have begun to shed light on how the plant is able to move in response to mechanical and chemical stimulation to envelop and digest prey. Individual tentacles, when mechanically stimulated, fire action potentials that terminate near the base of the tentacle, resulting in rapid movement of the tentacle towards the center of the leaf.^[16][17] This response is more prominent when marginal tentacles further away from the leaf center are stimulated. The tentacle movement response is achieved through auxin-mediated acid growth. When action potentials reach their target cells, the plant hormone auxin causes protons (H⁺ ions) to be pumped out of the plasma membrane into the cell wall, thereby reducing the pH and making the cell wall more acidic.^[18] The resulting reduction in pH causes the relaxation of the cell wall protein, expansin, and allows for an increase in cell volume via osmosis and turgor. As a result of differential cell growth rates, the sundew tentacles are able to achieve movement towards prey and the leaf center through the bending caused by expanding cells.^[19] Among some drosera species, a second bending response occurs in which non-local, distant tentacles bend towards prey as well as the bending of the entire leaf blade to maximize contact with prey. While mechanical stimulation is sufficient to achieve a localized tentacle bend response, both mechanical and chemical stimuli are required for the secondary bending response to occur.^[20]

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 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 heliotropic, moving in response to the sun's position in the sky.

The

The root systems of most Drosera are often only weakly developed or have lost their original functions.^[21] They are relatively useless for nutrient uptake, and they serve mainly to absorb water and to anchor the plant to the ground; they have long hairs.^[21]

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

D. intermedia and D. rotundifolia have been reported to form arbuscular mycorrhizae, which penetrate the plant's tissues,^[22] they also host fungi like endophytes to collect nutrients when they grow in poor soil and form symbiotic relationships.^[23]

Reproduction

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,

In culture, sundews can often be propagated through leaf, crown, or root cuttings, as well as through seeds.[15]

Distribution

The

.

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)".^[24] He particularly pointed to the absence of 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 America.^[24]

Habitat

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

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 them.

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 frost-resistant.

Conservation status

Protection of the genus varies between countries. None of the Drosera species in the United States are federally protected. Some are listed as threatened or endangered at the state level, but this gives little protection to lands under private ownership.^[25] Many of the remaining native populations are located on protected land, such as national parks or wildlife preserves.^[26] Drosera species are protected by law in many European countries, such as Germany, Austria, Switzerland, the Czech Republic, Finland, Hungary, France, and Bulgaria.^[27] In Australia, they are listed as "threatened".^[28] In South America and the Caribbean, Drosera species in a number of areas are considered critical, endangered or vulnerable, while other areas have not been surveyed.^[29] At the same time that species are at risk in South Africa,^[30] new species continue to be discovered in the Western Cape^[31] and Madagascar.^[32]

Worldwide, Drosera are at risk of extinction due to the destruction of natural habitat through urban and agricultural development. They are also threatened by the illegal collection of wild plants for the horticultural trade.^[30] An additional risk is environmental change, because species are often specifically adapted to a precise location and set of conditions.^[30]

Currently, the largest threat in Europe and North America is loss of wetland habitat.^[25][33] Causes include urban development and the draining of bogs for agricultural uses and peat harvesting.^[30] Such threats have 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 are closely tied to their geographical location.^[30] Increased legal protection of bogs and moors,^[34] and a concentrated effort to renaturalize such habitats, are possible ways to combat threats to Drosera plants' survival.^[35] As part of the landscape, sundews are often overlooked or not recognized at all.^[36][37]

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. The African sundews D. insolita and D. katangensis are listed as critically endangered by the International Union for Conservation of Nature (IUCN), while D. bequaertii is listed as vulnerable.^[25] Expanding population centers such as Queensland, Perth, and Cape Town, and the draining of moist areas for agriculture and forestry in rural areas threaten many such habitats. The droughts that have been sweeping Australia in the 21st century pose a threat to many species by drying up previously moist areas.^[30]

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.^[27][30]

Gallery of prey

• 
  Tipulidae (crane fly) trapped by Drosera filiformis
• 
  Moth, Phalaenophana pyramusalis (Dark-banded Owlet) trapped by Drosera filiformis
• 
  Eusarca confusaria moth trapped by Drosera filiformis
• 
  Tabanus fly trapped by Drosera filiformis
• 
  Drosophila melanogaster fly trapped by Drosera capensis

Uses

Traditional medicine

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.^[38] Culbreth's 1927 Materia Medica listed D. rotundifolia, D. anglica and

expectorants, and "of doubtful efficacy" for treating bronchitis, whooping cough, and tuberculosis.^[39]

Sundew tea was recommended by herbalists for dry coughs, bronchitis, whooping cough, asthma and "bronchial cramps".^[40] The French Pharmacopoeia of 1965 listed sundew for the treatment of inflammatory diseases such as asthma,

chronic bronchitis and whooping cough.^[41]

Drosera has been used commonly in cough preparations in Germany and elsewhere in Europe.

stomach ulcers.^[43]

Herbal preparations are primarily made using the roots, flowers, and fruit-like capsules.

Baltics

.

Sundews are historically mentioned as an aphrodisiac^[45] (hence the common name lustwort).^[46] They are mentioned as a folk remedy for treatment of warts, corns, and freckles.^[47]

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.^[48]

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

peat moss, sand, and/or perlite, and are watered with distilled, reverse osmosis, or rain water.^[15]

Nanobiotechnology

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.^[49] 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.^[49] 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.^[49] 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 biomaterial.^[50]

Other uses

The corms of the tuberous sundews native to Australia are considered a delicacy by the Indigenous Australians.^[12]: 100 Some of these corms were also used to dye textiles,^[51][52] while another purple or yellow dye was traditionally prepared in the Scottish Highlands using D. rotundifolia.^[53] 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.^[52]

Chemical constituents

Several chemical compounds with potential biological activities are found in sundews, including

ascorbic acid

(vitamin C).

References

1. ^ ^{a b} "Drosera L." Plants of the World Online. Royal Botanic Gardens, Kew. 2023. Retrieved 13 January 2023.
2. ^ McPherson, S.R. (2010). Carnivorous Plants and their Habitats. Poole, England, UK: Redfern Natural History Productions Ltd. 2 volumes.
3. ^ McPherson, S.R. (2008). Glistening Carnivores. Poole, England, UK: Redfern Natural History Productions Ltd.
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8. ^ Liddell, Henry George; Scott, Robert (1940). "δρόσος". A Greek-English Lexicon. Perseus Digital Library.
9. ^ Darwin, the Elder, Robert Waring (1787). Principia Botanica; Or, A Concise and Easy Introduction to the Sexual Botany of Linnæus, Etc. [The Preface Signed: R. W. D., I.e. Robert W. Darwin, the Elder.]. Newark: Allin & Company. Retrieved 14 March 2022.
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11. ^ Mann, Phill (2001). "The world's largest Drosera". Carnivorous Plant Newsletter. 30 (3): 79. Archived from the original on 2011-09-29. Retrieved 2022-08-17.
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27. ^ ^{a b} Baranyai, B.; Jooste, H. (2016). "Biology, ecology, use, conservation and cultivation of round-leaved sundew (Drosera rotundifolia L.): a review" (PDF). Mires and Peat. 18: 1–28.
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38. ^ "Drosera herba". Altmeyers Encyclopedia - Department Phytotherapy. 29 October 2020. Retrieved 17 March 2022.
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45. ^ Wolf, E.; Gage, E.; Cooper, D.J. (29 June 2006). "Drosera rotundifolia L. (roundleaf sundew): a technical conservation assessment" (PDF). USDA Forest Service, Rocky Mountain Region. Retrieved 17 March 2022.
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Further reading

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 (2007). The curious world of carnivorous plants : a comprehensive guide to their biology and cultivation (English language ed.). Portland, Or.: Timber Press.
  ISBN 978-0881927924
  .
• Correa A., Mireya D.; Silva, Tania Regina Dos Santos: Drosera (Droseraceae), in: Flora Neotropica, Monograph 96, New York, 2005
• Lowrie, Allen: Carnivorous Plants of Australia, Vol. 1–3, English, Nedlands, Western Australia, 1987–1998
• Lowrie, A. (2005). "A taxonomic revision of Drosera section Stolonifera (Droseraceae), from south-west Western Australia" (PDF). Nuytsia. 15 (3): 355–393.
• Olberg, Günter: Sonnentau, Natur und Volk, Bd. 78, Heft 1/3, pp. 32–37, Frankfurt, 1948
• 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

Look up Sundew in Wiktionary, the free dictionary.

• A key to Drosera species, with distribution maps and growing difficulty scale
• A virtually exhaustive listing of Drosera pictures on the web
• International Carnivorous Plant Society
• Carnivorous Plant FAQ
• The Sundew Grow Guides
• Sundew images from smugmug
• Botanical Society of America, Drosera - the Sundews Archived 2010-06-13 at the Wayback Machine