Impatiens — touch-me-nots: natural history, characteristics, and cultivation

Impatiens is a large genus of roughly 850–1000 species of flowering plants, found across much of the Northern Hemisphere and in tropical regions worldwide (tropics). Together with the single species Hydrocera triflora, these plants form the family Balsaminaceae. Species vary from low, ephemeral annuals to clump-forming perennials and shrubs in shaded, moist habitats such as forest understories, stream banks and damp clearings.

The common name "touch-me-not" and the scientific epithet Impatiens derive from the Latin for "impatient." This refers to the distinctive fruit: a fleshy capsule that, when ripe, ejects its seeds with sudden force. The mechanism, known as explosive dehiscence, can propel seeds several metres and is an example of rapid plant movement; it aids wide dispersal in dense habitats and reduces competition near the parent plant (Latin origin, seed capsules, rapid movement).

Morphologically, impatiens typically have succulent or brittle stems, alternate simple leaves, and asymmetrical (zygomorphic) flowers often with a pronounced nectar spur. Flowers occur in a broad palette of colors — white, pink, red, purple, orange and yellow — and are adapted to a range of pollinators including bees, butterflies and, in the Americas, hummingbirds. Many species are short-lived in cultivation but set seed readily, while others form persistent clumps in perennial borders.

Several species have become important in horticulture. The familiar bedding plant "Busy Lizzie" is Impatiens walleriana, native to parts of East Africa; it and New Guinea impatiens (I. hawkeri) are parents of many garden hybrids. I. walleriana was selectively bred for garden use by growers such as Claude Hope, who developed early series of compact cultivars known as the Elfin and later Super Elfin series. Hybridization produced varieties with varied flower forms, some double-flowered, and a wide color range; New Guinea hybrids are often chosen for better heat tolerance and larger blooms.

Impatiens have both benefits and challenges in cultivation and ecology. They are valued for shade bedding, containers and hanging baskets because of their profuse flowering and tolerance for low light. However, some species can escape gardens and become invasive in island or tropical ecosystems; for example, certain popular bedding impatiens have naturalized and become problematic in places such as Hawaiʼi. Diseases such as downy mildew have also affected garden populations, encouraging growers to select resistant cultivars or alternative species.