Impatiens (pronounced /ɪmˈpeɪʃənz/)[1] is a genus of about 850–1,000 species of flowering plants, widely distributed throughout the Northern Hemisphere and tropics. Together with the puzzling Hydrocera triflora, this genus makes up the family Balsaminaceae. Such a situation is highly unusual, and phylogenetic studies might reveal that Impatiens needs to be split up; some of its species might be closer to Hydrocera than to their presumed congeners.
Common names include impatiens, jewelweeds, and, somewhat ambiguously, "balsams" and "touch-me-nots". 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 commonly planted in horticulture have altogether more fanciful names, such as "Busy Lizzie" (the well-known I. walleriana).
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[edit] Description
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 under the leaf surface, giving them a silvery sheen that becomes pronounced when held under water. The name "jewelweed" possibly refers to these shiny leaves, particularly obvious after rains when water drops reflect the sunlight like a prism. However it is more likely that the name is derived from the robin egg blue of the surface of the seed beneath the dark brown aril, or seed coat.
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.
Ecology and uses
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)
A parasitic plant using balsams as host is the European Dodder (Cuscuta europea). For plant diseases affecting this genus, see List of impatiens diseases.
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[2], 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.
Hybrids, typically derived from Busy Lizzie (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 was originally collected from Costa Rica (where it grows as a weed), and 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 Hawaiʻi, 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.
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.
Medical significance and phytochemistry
The North American jewelweeds are often used as a home remedy to treat bee stings, insect bites, and particularly Poison Ivy (Toxicodendron radicans) and Stinging Nettle (Urtica dioica) rashes, but there has not been controlled research to support this application.
An oft-repeated folk saying, "Wherever poison ivy is found, jewelweed grows close by", is not true. Poison ivy grows in a wide variety of habitats, while jewelweeds are restricted to moist bottomlands and valleys with rich soil. The reverse is often true on the other hand: wherever jewelweed is found, poison ivy is usually close by[citation needed].
The Orange and the Yellow Jewelweed (I. pallida) have been subject to various scientific studies as regards their alleged effect against Poison Ivy contact dermatitis. Save for one study conducted in the 1950s[3], no significant and lasting antipruritic effect was found compared to other commonly used treatments[4].
Jewelweed contains 2-methoxy-1-(4-naphtho)quinine, an anti-inflammatory and fungicide that is the active ingredient of Preparation H [5].
Unspecified Impatiens is one of the traditional 83 Bach flower remedies, supposedly alleviating impatience, and is contained in the "Rescue Remedy" or "Five Flower Remedy" touted as an anxiolytic. There is no indication that Bach flower remedies are more effective than a placebo[citation needed].
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[6]. 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. 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).
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