I have never found a really good
weed chart anywhere.
It sounds like you have oxalis of a weedy sort. It is an opportunistic
weed for sure. You may need to reapply your
weed killer several times to get rid of it. it has more roots than it has green growth above ground.
Make sure you read the directions on the
weed killer. That is where most people lose the effectiveness. Like watering too soon afterwards and washing it off the leaves.