Codariocalyx motorius (though often placed in Desmodium), known as the telegraph plant or semaphore plant, is a tropical Asian shrub, one of a few plants capable of rapid movement; others include Mimosa pudica and the venus flytrap.
It is widely distributed throughout Bangladesh, Bhutan, Cambodia, China, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Pakistan, Sri Lanka, Taiwan, Thailand and Vietnam. It can even be found on the Society Islands, a remote chain of islands in the South Pacific. It produces small, purple flowers. This plant has small, lateral leaflets which move at speeds rapid enough to be perceivable with the naked eye. This is possibly a strategy to maximise light by tracking the sun. Each leaf is equipped with a hinge that permits it to be moved to receive more sunlight, but the weight of these leaves means the plant must expend a lot of energy in moving it. To optimise its movement, each large leaf has two small leaflets at its base. These move constantly along an elliptical path, sampling the intensity of sunlight, and directing the large leaf to the area of most intensity. Another hypothesis has been offered that the rapid movements are intended to deter potential predators.
The common name is due to the rotation of the leaflets with a period of about three to five minutes; this was likened to a semaphore telegraph, a structure with adjustable paddles that could be seen from a distance, the position of which conveyed a message in semaphore, hence the common names.
The plant is described in detail in Charles Darwin's 1880 The Power of Movement in Plants.