Some plants in the pea family have a rather unusual ability that sets them apart from the rest of the plant world. They can collapse their leaves and stems when touched or disturbed in some way. The best known of these ‘sensitive plants’ is Mimosa pudica, a tropical weed that comes from South and Central America.
It is a complex process that happens within the plant’s cells that provide support to the leaves and stems. The cells are filled with water, which keeps them turgid and firm, when the plant is touched the cells release the water deflating them, resulting in the leaves and stems to collapse and fold inwards… if you watch closely, a few minutes later the water will be pumped back and they will return to normal.
So why do they do it? Plants have to come up with many clever ways to stop themselves being munched on by animals and insects, as they can’t run away and hide! So the drooping leaves will deter hungry animals and hopefully shake off insects. The sensitive plant also comes in quite useful if you get bitten by a monocled Cobra snake, the extracts from the roots can be used to counteract the venom.
Answered by Wesley Shaw, keeper of the Palm House, Royal Botanic Gardens, Kew.