Of course cultivated carrots come in many forms, the hairy stems you show I have seen on some rogue carrots which usually have a not so orange root, more often a yellow root which looks to be a throw back to the wild form.
Carrots do make flower heads of course, or you wouldn't be able to buy the seeds. This is what your 'weed' looks like to me.
http://en.wikipedia.org/wiki/C...
