The Mimosa, or Silk Tree, looks to me like a beautiful tropical tree. It seems almost too delicate for a New England resident. Years ago, way back when I was a groundskeeper, I remember one of the farmers bringing in Mimosa seedlings and mentioning that the leaves would close up at night. I didn't pay much mind then but never forgot the delicate leaves. The little quote below seems to support this behavior although I can find no confirming sources.
"But stay; here is surely death in the midst of all this glorious life—a mimosa-tree, whose leaves, though green, are closed and drooping as if all vitality were withdrawn. We look at the root—no disturbance has been there ; at branches, leaves, blossom—all seem perfect, though paralysed and unconscious as if with the blight of death.
"Death, or only sleep ? As we watch and wonder the slanting rays of yellow light from the great sun, hidden hitherto by the mountain opposite, creep towards us. They touch our mimosa-tree, and at the same moment we hear the rustle of the morning breeze among its leaves. Even as we look the delicate twigs are stirred; they flutter in the wind; they lift themselves to the golden sun-rays; and ere we pass on the leaves are expanded, the blossoms erect, and the tree seems to rejoice among its fellows in its gracious fulness of life."
Carus-Wilson, Ashley. Irene Petrie, Missionary to Kashmir. London, 1901. 140. Web. Google Book Search. 6 Aug 2009.