On 5 Sep 2005 21:55:16 -0700, "Daniel_B" wrote:

Hello, I live in the midwest, IL., USA. I was visiting my brother and
his family today and noticed a very strange plant I have never seen
before growing in one of their outside flower pots. I asked my sister
in-law about it and she said it just startd growing a couple of weeks
ago and she decided not to pull it out. My other brother who was also
there and is an avid gardener said he had never seen this type of plant
either. The plant is about a foot high now. It has lots of stems with
leaves that, when the sun is on them, open up. When I saw it, the plant
was in shade and the leaves were folded up, kind of like a zipper. Each
leaf is about a 1/4 inch length. The whole plant is the same color of
green. I would say about the same shade of green as a tomatoe plant
leaf.

Sounds like a mimosa tree. Not genus Mimosa, but I don't remember
what it is.