The rain tree is a mimosa plant of the tropics of Central and South America. It is named rain tree because it seems to rain lightly under its crown at night. The grass under the tree stays green much longer in the dry season. It is possible that the tree-dwellers are responsible for this phenomenon. The tree also has the peculiarity of folding its leaflets together when it rains, so that the water droplets barely fall through the crown. That could explain the green grass as well.