The telegraph plant (Desmodium gyrans, also known as Codariocalyx motorius), is very strange. At the base of its larger paddle-shaped leaves are smaller leaflets that can be seen constantly twitching around in circles during the day for no obvious reason. These elliptical movements are driven by special motor cells at the base of each leaflet expanding and contracting with water – the movements grow faster with increasingly bright light or increasing temperatures. At around 35C, the leaflets can make one rotation every 90 seconds or so.
Charles Darwin in 1881 called it a “vegetable wonder” but was baffled by the plant’s movements. “No one supposes that the rapid movements of the lateral leaflets of [Desmodium gyrans] are of any use to the plant; and why they should behave in this manner is quite unknown.”
Since then, attempts have been made to explain why the leaflets move – including tracking the sun to help the main leaves find the best light, deterring butterflies from laying their eggs by imitating the flapping of insect wings to look as if the plant is already occupied, or simply putting off insects from eating the plant – but it remains a mystery.
