It’s fun to touch the sensitive plant, Mimosa pudica, and watch the leaflets close up in response. For the plant though, this defensive reaction is energy consuming. If the plant “learns” a certain continuing stimulus is not particularly damaging, it will cease to close its leaves. Scientists in Australia and Italy found mimosa plants became habituated to continuous dripping water more quickly in an unfavorable growing environment than in a favorable one. Surprisingly, the memory of this stimulus, along with the conditioned behavior of not closing its leaves, persisted for a month even when the plant was moved to a favorable growing environment and left undisturbed.
Oecologia, published online January 05, 2014