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swanflower

Aristolochia

Aristolochia is a large plant genus with over 500 species. Collectively known as birthworts, pipevines or Dutchman's pipes, they are the namesake of the family (Aristolochiaceae). They are widespread and occur in the most diverse climates, but they are not native to Australia. Some species, like A. utriformis and A. westlandii, are threatened with extinction.

Description

Aristolochia is a genus of evergreen and deciduous woody vines and herbaceous perennials. The smooth stem is erect or somewhat twining. The simple leaves are alternate and cordate, membranous, growing on leaf stalks. There are no stipules.

The flowers grow in the leaf axils. They are inflated and globose at the base, continuing as a long perianth tube, ending in a tongue-shaped, brightly colored lobe. There is no corolla. The calyx is one to three whorled, and three to six toothed. The sepals are united (gamosepalous). There are six to 40 stamens in one whorl. They are united with the style, forming a gynostemium. The ovary is inferior and is four to six locular.

These flowers have a specialized pollination mechanism. The plants are aromatic and their strong scent attracts insects. The inner part of the perianth tube is covered with hairs, acting as a fly-trap. These hairs then wither to release the fly, covered with pollen.

The fruit is dehiscent capsule with many endospermic seeds.

The common names "Dutchman's Pipe" and "Pipevine" (e.g. Common Pipevine, A. durior) are an allusion to old-fashioned meerschaum pipes at one time common in the Netherlands and Northern Germany. "Birthwort" (e.g. European Birthwort, A. clematitis) refers to these species' flower shape, resembling a birth canal. Some reference books state that the scientific name Aristolochia was developed from Ancient Greek aristos (άριστος) "best" + locheia (λοχεία), "childbirth" or "childbed".

Medical use and toxicity

A. clematitis was highly regarded as a medical plant since the ancient Egyptians, Greeks and Romans, and on to until the Early Modern era; it plays also a minor role in Traditional Chinese Medicine (TCM). It is however most notable for containing toxic aristolochic acid, sometimes in quantities fatal to humans.

Due to the Doctrine of signatures "birthwort" was used in childbirth. A preparation was given to women in labor to expel the placenta, but the aristolochic acid may just as well kill the patient.

Virginia Snakeroot (A. serpentaria) is thus named because the root was used to treat snakebite, also with a rather uncertain degree of success. A. pfeiferi, A. rugosa and A. trilobata are also used in folk medicine to cure snakebites. Aristolochic acid does indeed appear to bind and deactivate the Phospholipase A2 of certain snake venoms.

Others claim that a decoction of birthwort stimulates the production and increases the activity of leukocytes (white blood cells), or that pipevines contain a disinfectant which assists in wound healing. Aristolochia bracteolata is colloquially known as "Worm Killer" due to supposed antihelminthic activity.

Epidemiological and laboratory studies have shown the toxicity of herbal remedies containing plant species of the genus Aristolochia. Herbal compounds containing Aristolochia are classified as a Group 1 carcinogen by the International Agency for Research on Cancer.

In July 1999, two cases of nephropathy associated with the use of Chinese botanical preparations were reported in the United Kingdom. These preparations were shown to contain aristolochic acid. Biopsy samples showed extensive loss of cortical tubules with interstitial fibrosis. In 1993, a series of end-stage renal disease cases had been reported from Belgium associated with a weight loss treatment, where Stephania tetrandra in a herbal preparation was suspected of being substituted with Aristolochia fangchi. More than 105 patients were identified with nephropathy following the ingestion of this preparation from the same clinic from 1990-1992. Many required renal transplantation or dialysis. Subsequent follow up of these patients has shown they are at an increased risk of urological cancer. Note that in TCM neither plant is used for prolonged weight loss treatments.

It appears as if contamination of grain with European Birthwort (A. clematitis) is a cause of Balkan nephropathy, a severe renal disease occurring in parts of southeastern Europe.

Other uses

Due to their spectacular flowers, several species are used as ornamental plants.

Many species of Aristolochia are food for larvae of Lepidoptera, namely swallowtail butterflies. These become unpalatable to most predators by eating the plants. Lepidoptera feeding on pipevines include:

Choreutidae

Papilionidae

Nymphalidae

Selected species

Formerly placed here

See also

Footnotes

References

External links

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