Dandelion. For future reference it is really helpful to state where the plant is growing to get an id. Luckily (for id purposes) Dandelions are ubiquitous so it's easy.

On your other post there are two plants in the photo and no indication of location. That makes it tough.

Thanks for the advice and answer!

please see one of your other threads on same topic.
http://forums.gardenweb.com/discussions/2965069/natural-solutions-for-this-patch-possibly-chickweed?n=2

HINT: Keep all questions about the same topic in the original/same thread.