1. Impatiens L. (jewelweed, touch-me-not)

Plants annual herbs (perennial elsewhere). Stems ascending, often somewhat succulent, simple or branched, hollow between the nodes, the nodes usually somewhat swollen. Leaves alternate (opposite or whorled elsewhere), mostly petiolate, the blades simple, the margins finely toothed or scalloped. Stipules absent. Inflorescences axillary, the flowers solitary or 2–5 in small clusters or panicles, some of the flowers usually small and nonopening (cleistogamous). Flowers zygomorphic, perfect, hypogynous, stalked, twisted at the base during development so that the top of the flower is oriented toward the bottom at maturity (resupinate). Sepals 3, the apparent lowest one petaloid and inflated into a conical pouch, this tapered to a slender nectar-producing spur that is usually recurved or strongly bent at maturity, the two lateral sepals 2–7 mm long, free, somewhat cupping the flower, broadly and obliquely ovate, tapered abruptly to a sharply pointed tip, and green or pale-colored. Petals 5, but appearing as 3, each of the 2 apparent lateral ones lobed, representing a fused pair, the single apparently upper petal free, wider than long, and keeled. Stamens 5, the filaments short and flat, fused toward the tips, each with a scalelike appendage on the inner side, these appendages fused into a cap over the pistil, the short, stout anthers often also somewhat fused, the whole complex of stamens and cap shed as a unit before the stigmas mature. Pistil 1 per flower, of 5 fused carpels, the ovary superior, 5-locular, the placentation axile. Ovules 3 to many per locule. Style absent or very short, the stigmas 5, minute. Fruits capsules, the 5 fleshy valves elastic, coiling violently from the base to the tip at dehiscence, scattering the seeds. Four hundred to 850 species, North America, Central America, Caribbean Islands, Europe, Africa, Asia, south to Java.

The common name touch-me-not refers to the intriguing explosive dehiscence of the capsules when touched, a trait that makes a patch of fruiting plants irresistible to children of all ages; hence, they are among our most familiar native wildflowers. The name jewelweed apparently refers to the shiny, silvery appearance of the wet foliage. The juice from crushed plants is reputed to counteract the itching effects of chiggers, mosquito bites, and poison ivy when rubbed on the skin. Native Americans had multiple medicinal uses for species of Impatiens, including as treatments for dermatitis, burns, fever, and gastrointestinal ailments; they also boiled plants for use as dyes (Moerman, 1998). Several species are cultivated as ornamentals. The native species are easily grown in moist soil of sunny locations but can spread aggressively by seeds.