I just moved into this place and the back yard was in much disarray and chaos. I spent all weekend digging out weeds because you couldn't pull them up. I had to use a shovel and dig them up.

The looked similar to Holly Hocks, but instead of a flower they have seeds and while digging them up I dropped seeds everywhere. The sod has choked them out except the edges of the concrete patio where they're pushing their way up. The roots are about 1/2" round, white-ish, and fiberous. They go deeper than my 8" spade and I can't seem to pull them up.

Have you ever seen anything like this?