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|Impatiens scapiflora at|
Silent Valley National Park, South India
850–1,000; see text
|Impatiens scapiflora at|
Silent Valley National Park, South India
850–1,000; see text
Impatiens // is a genus of about 850–1,000 species of flowering plants, widely distributed throughout the Northern Hemisphere and tropics. Together with Hydrocera triflora, impatiens make up the family Balsaminaceae.
Common names include impatiens, jewelweed, touch-me-not, snapweed, and, for I. walleriana in Great Britain, "busy lizzie", as well as, ambiguously, balsam. As a rule-of-thumb, "jewelweed" is used exclusively for Nearctic species, "balsam" is usually applied to tropical species, and "touch-me-not" is typically used in Europe and North America).
Some species are annual plants and produce flowers from early summer until the first frost, while perennial species, found in milder climates, can flower all year. Regardless of their lifespan, the largest impatiens grow up to about 2 meters (c. 7 ft) tall, but most are less than half as tall. The leaves are entire and shiny; their upperside has a thick, water-repellent cuticula that gives them a greasy feel. Particularly on the underside of the leaves, tiny air bubbles are trapped over and under the leaf surface, giving them a silvery sheen that becomes pronounced when held under water.
The flowers, up to 2–3 cm, around 1 inch long, in most species are made up by a shoe- or horn-shaped spur for the most part, with at least the upper petals insignificant by comparison; some have a prominent labellum though, allowing pollinators to land. Others, like the Busy Lizzie (I. walleriana), have flattened flowers with large petals and just a tiny spur that appear somewhat similar to violets (Viola), though these are unrelated eudicots. A few Impatiens species have flowers quite intermediate between those two basic types.
These plants derives their scientific name Impatiens (Latin for "impatient") and the common name "touch-me-not" in reference to their seed capsules. When the capsules mature, they "explode" when touched, sending seeds several meters away. This mechanism is also known as "explosive dehiscence"; see also Rapid plant movement.
Balsams grow both in and out of direct sunlight; they prefer moist, rich soils, like roadside ditches, reed beds, fens, river banks and forest edges, and many are well able to colonize disturbed ruderal locations.
Impatiens foliage is used as food plants by the larvae of some Lepidoptera species (e.g. Dot Moth, Melanchra persicariae), as well as other insects, such as the Japanese Beetle (Popillia japonica). The leaves are toxic to many other animals, including the Budgerigar (Melopsittacus undulatus), but this popular pet will eat balsam flowers eagerly and as it seems it is not harmed by them. The flowers are visited by bumblebees and certain Lepidoptera, such as the Common Spotted Flat (Celaenorrhinus leucocera)
In the 19th and 20th centuries, humans transported the Orange Jewelweed (I. capensis) to England, France, the Netherlands, Poland, Sweden, Finland, and potentially other areas of Northern and Central Europe. For example, it was not recorded from Germany as recently as 1996, but since then a population seems to have established itself in Hagen at the Ennepe river. These naturalized populations persist despite the plant not being grown in gardens on a regular basis. The Orange Jewelweed is quite similar to the Touch-me-not Balsam (I. noli-tangere) – the only Impatiens species native to Central and Northern Europe – and utilizes similar habitats, but no evidence exists of natural hybrids. Small Balsam (I. parviflora), originally native to southern Central Asia, is even more extensively naturalized in Europe. More problematic is the Himalayan Balsam (I. glandulifera), a high-growing species which displaces smaller plants by denying them sunlight. It is an invasive weed in many places, and tends to dominate riparian vegetation along polluted rivers and nitrogen-rich spots. Thus, it exacerbates ecosystem degradation by forming stands where few other plants can grow, and by rendering riverbanks more prone to erosion as it has only a shallow root system.
The starkly differing flower shapes found in this genus, combined with the easy cultivation of many species, have served to make some balsam species model organisms in plant evolutionary developmental biology. Also, Impatiens is rather closely related to the carnivorous plant families Roridulaceae and Sarraceniaceae. Peculiar stalked glands found on balsam sepals secrete mucus and might be related to the structures from which the prey-catching and -digesting glands of these carnivorous plants evolved. Balsams are not known to be protocarnivorous plants however.
The North American jewelweeds are often used as an herbal remedy for the treatment of bee stings, insect bites, and Stinging Nettle (Urtica dioica) rashes. They are particularly used after Poison Ivy (Toxicodendron radicans) contact to prevent a rash from developing. The efficacy of Orange Jewelweed (I. capensis) and Yellow Jewelweed (I. pallida) in preventing contact dermatitis has been subject to various scientific studies as regards its alleged effects against Poison Ivy contact dermatitis with conflicting results.
A study in 1958 found that jewelweed was an effective alternative to standard treatment  while later studies  found that jewelweed had no antipruritic effects after the rash has developed. Researchers reviewing these contradictions  state that potential reason for these conflicts include the method of preparation and timing of application. A 2012 study found that while jewelweed extract made from Orange Jewelweed (I. capensis) was not effective in reducing the effects of contact dermatitis, the application of jewelweed mash (made by chopping freshly harvested plants in a blender) was effective in decreasing the development of contact dermatitis.
Unspecified Impatiens is one of the traditional 83 Bach flower remedies, alleviating impatience, and is contained in the "Rescue Remedy" or "Five Flower Remedy" touted as an anxiolytic..
All Impatiens taste bitter and seem to be slightly toxic upon ingestion, causing intestinal ailments like vomiting and diarrhea. The toxic compounds have not been identified but are probably the same as those responsible for the bitter taste; they might be glycosides or alkaloids.
α-Parinaric acid, a polyunsaturated fatty acid discovered in the seeds of the Makita Tree (Atuna racemosa), is together with linolenic acid the predominant component of the seed fat of Garden Balsam (I. balsamina), and perhaps other species of Impatiens. This is quite intriguing from a phylogenetic perspective, since the Makita Tree is a member of the Chrysobalanaceae and belongs to a lineage of eudicots entirely distinct from the balsams.
At least certain jewelweeds and the Garden Balsam contain the naphthoquinone lawsone, a dye that is also found in Henna (Lawsonia inermis) and responsible for the hair coloring and skin coloring in mehndi. In ancient China, Impatiens petals mashed with rose and orchid petals and alum were used as nail polish: after leaving the mixture on the nails for some hours, it will color them a pink to reddish hue. In Korea, girls and women dye their fingernails overnight with bruised red balsam petals in summer, when balsam flowers are in full bloom. Traditional purpose of fingernail dying was to scare bad spirits, considering that spreading of cholera or any other contagious waterborne diseases were thought to be deeds of bad spirits. Similar to the case of α-Parinaric acid, the henna plant is a Lythraceae and as such also not closely related to the balsams.
Note that the "balsams" used in shampoos (Peru balsam and Tolu balsam) are derived from the unrelated genus Myroxylon, as are Canada balsam (from the Balsam Fir, Abies balsamea) and Balsam of Mecca (from Commiphora gileadensis).
Impatiens have become one of the most popular garden annuals. Hybrids, typically derived from "Busy Lizzie" (the well-known I. walleriana) and New Guinea Impatiens (I. hawkeri), have commercial importance as garden plants with a yearly business volume[where?] of about US $230 million. I. walleriana is native to East Africa, and was bred through selection by Claude Hope. The original series of impatiens bred by Hope was the 'Elfin' series of cultivars, which was subsequently improved as the 'Super Elfin' series. Double-flowered cultivars also exist. But in tropical islands, such as Hawaii, Busy Lizzie can also become a noxious weed.
Other Impatiens species, such as I. auricoma, Garden Balsam (I. balsamina), Blue Diamond Impatiens (I. namchabarwensis), Parrot Flower (I. psittacina), Congo Cockatoo (I. niamniamensis), Ceylon Balsam (I. repens) or Poor Man's Rhododendron (I. sodenii) are also often seen as ornamental plants. Note that insecticidal soap, commonly used against insect pests as it is less harmful to the environment and to most beneficial insects than halocarbon insecticides, is very toxic to some balsams. When controlling insect pests on Impatiens, insecticidal soap should be avoided.
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