where do you live?

Take a look at this: http://ipm.ucanr.edu/PMG/WEEDS/yellow_nutsedge.html

North of Houston, Tx

Wherever you live, it's a weedy sedge.

You might send images to your county's Extension Service Office where they are likely to provide you with a precise ID and management suggestions within minutes. Locate that office using this interactive map:

http://npic.orst.edu/pest/countyext.htm

Dene: I'm on the other side of town (SW Houston), and it looks a lot like what I had/have in my yard: kyllinga. See the pics about halfway down. I used Image on the lawn early last month and it seems to have done the trick. I'll have to survey and take a closer look this week. Good luck.

Green Kyllinga info: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7459.html