Virginia Morell in Lapham’s Quarterly:
A member of the pea family, M. pudica is a small plant with tiny leaflets paired along the length of each stem and pretty lavender-pink globular flowers. The leaves give it a fernlike, feminine look, although it is also armed with thorns to ward off attacks. It’s native to Central and South America but has spread throughout the tropics partly because of its popularity as a novel ornamental that exhibits a fascinating behavior: if you touch a single leaf, the plant will swiftly fold up all its leaves before your eyes. Only a soft touch is required to bring on this collapse; after a while, you can also watch as the wilted-appearing mimosa sets about righting itself and reopening its leaves. You may have discovered the mimosa’s animal-like trick in an arboretum or store where the plants are sometimes displayed or sold. The rapid response to being touched is another defensive tactic—it startles most insects, as it does naive humans.
M. pudica and its curious actions were known to Western science even before 1753, when Linnaeus officially named the species. Many leading scientists of the day, including Robert Hooke (the English natural philosopher best known for being the first to see and describe a cell via a microscope) and later the French naturalist Jean-Baptiste Lamarck studied the plant. Lamarck was particularly struck by how mimosas eventually no longer respond to being repeatedly touched.