Touch-me-nots fling their seeds several metres with an exploding pod
Impatiens means impatient in Latin, and the name is earned. Ripe seed capsules split open violently at the slightest touch, hurling seeds up to several metres away. That explosive trick gives the genus its other nicknames, touch-me-not and snapweed, and helps explain how some species spread so fast.
The genus is huge, with more than 1,000 species across the Northern Hemisphere and the tropics, most of them in mountain forests of Africa, Madagascar, the Himalayas, southwest India's Western Ghats and southeast Asia. Only one species, Impatiens noli-tangere, is native to Europe. Most are soft-stemmed herbs between five centimetres and 2.5 metres tall, though a few in southeast Asia grow into shrubs or small trees. Air trapped on the undersides of the leaves gives them a silvery sheen, striking when held underwater.
The flowers are built to avoid self-pollination. Each starts male, with fused stamens forming a cap over the ovary; the cap drops off and only then does the stigma become receptive. Flower shapes vary so much that species are often grouped by pollinator, from bumblebees and butterflies to moths, flies and sunbirds. Madagascar has a group of about 125 species with no nectar spur at all. That diversity, plus easy cultivation, has made some balsams model organisms for studying how plant forms evolve.
People have moved several species around. North American orange jewelweed was carried to Britain, France, Sweden and other countries in the 19th and 20th centuries, and it was unrecorded in Germany as recently as 1996 before a population settled along the Ennepe River at Hagen. Britons know Impatiens glandulifera as policeman's helmet and the popular garden plant I. walleriana, from East Africa, as busy lizzie. Between 2011 and 2013 an outbreak of downy mildew hit impatiens hard in the United States.
Chemistry adds surprises. Garden jewelweed contains lawsone, the same dye found in henna, and in ancient China mashed impatiens petals with alum were used to stain fingernails pink or red. All species taste bitter and are mildly toxic if eaten, and a study of Rescue Remedy, which includes I. glandulifera, found no difference from a placebo.
Source: Impatiens
