I have a weed growing in my St. Augustine lawn grass that I have been unable to identify.The weed has, over the past several weeks, appeared to spread out even after we spent time trying to pull it out. Actually, trying to pull it out doesn't work as the stems are fine and difficult to grasp low enough to get root. I took several photos of it but I haven't been able to find a corresponding photo by Internet search. Any advice would be appreciated.

A local horticulturist could not identify the plant, but did say that it appears to be a grass and that Atrazine would not work on it. She went on to say that any herbicide used to kill it would also affect our Floratam St. Augustine grass.

I would appreciate any other comments or advice.