Sensitive plants fold their leaves inward within seconds of being touched, then reopen a short time later.

The longer version

Touch triggers a rapid change in water pressure inside cells at the base of each leaflet. Ions move across membranes, water follows, and the cells lose stiffness, so the leaflets collapse inward and the whole leaf droops within a second or two.

Reopening takes longer, because the plant has to pump water back in and restore pressure. The response appears to discourage grazing insects and to limit damage from heavy rain or wind. Repeated stimulation tires the mechanism temporarily, and the plant becomes less responsive for a while. Related species use the same mechanism at different speeds, and some respond to heat as well as touch.

Where this entry sits

Plants and Trees gathers ordinary and surprising details about how green things live, from the tallest forest giants down to the moss on a garden wall. Expect notes on flowers, seeds, roots, leaves, fungi, and the quiet tricks plants use to spread and survive. The full list sits on the Plants and Trees page, where every entry is listed in order.