Jewelweed is a North American common name for a number of species of flowering plant in the genus Impatiens, family Balsaminaceae, native to eastern North America. They typically grow about 1 to 1.5 m tall, and die after one season. Like other Impatiens, jewelweed is notable for having seed pods that burst when touched ("spring-loaded seeds"), spreading seeds over several square meters. Because of this, it also has the common name (shared with many other Impatiens species) of Touch-me-not. Jewelweed is often used as a home remedy to treat poison ivy rashes, but has been shown not to have any anti-itch properties in several controlled studies.
Species called jewelweed include:
These species grow in moist, rich soils in valleys and stream-bottoms. Pale jewelweed tends to grow slightly taller and to tolerate somewhat shadier sites than orange jewelweed, while the latter is more common and better able to grow in disturbed areas.
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 jewelweed is restricted to moist bottomlands and valleys with rich soil. The reverse is often true: wherever jewelweed is found, poison ivy is usually close by. Jewelweed grows in sunny, wet areas, such as roadside ditches and fens.
Jewelweed's 1 cm (½ inch) long flowers are shaped like a shoe. Some plants have orange flowers with dark spots, while others have plain yellow flowers. When held under water, the leaves appear silvery in color (most noticeably on the underside of the leaf) due to tiny air bubbles trapped across the leaf surface. Also, when water collects on the leaves of the Jewelweed, it tends to clump together because of the smooth texture of the leaves. White light can then be refracted through the prism, thus presenting the color spectrum, giving it the appearance of a jewel. These two characteristics possibly explain the plant's common name.
In the 19th and 20th centuries, humans transported the Orange Jewelweed (Impatiens capensis) to England, France, the Netherlands, Poland, Sweden, Finland, and potentially other areas of Northern and Central Europe. These naturalized populations persist in the absence of any common cultivation by people. The orange jewelweed is quite similar to Impatiens noli-tangere, an Impatiens species native to Europe and Asia. No evidence exists of natural hybrids, although the habitats occupied by the two species are very similar. There are currently no records of pale jewelweed being cultivated outside North America, nor are there documented naturalizations.
Jewelweed has been shown to be devoid of any anti-itch activity (antipruritic effect) in several controlled studies, but is still used widely as a home remedy against poison ivy rashes, bee stings, and insect bites. Jewelweed contains the naphthoquinone lawsone, a dye that is also found in Henna and that is responsible for the permanent hair coloring and skin coloring in mehndi.