850–1,000; see text
Impatiens (pronounced /ɪmˈpeɪʃənz/) 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).
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.
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