Took a piece of this from cousin's flower beds not sure what is, any ideas?

Thanks for the help in advance.

Conoclinium coelestinum (Blue mistflower) ?

http://www.wildflower.org/plan...

I'm not familiar with Conoclinum, I was thinking Ageratum. How would you tell the difference? I assume because Scott took a piece, implying perennial, rather than a plant, implying an individual in an annual bedding display?

Ageratum:
https://www.google.ca/search?q...

Thanks again for all the help. Sooby the annual is very similar, and can't speak for those who pointed me in right direction would agree that my comment led to perennial rather than annual, but also looking at both pictures think the leaf Conoclinium coelestinum (Blue mistflower) a little more saw toothed on edge than the Ageratum can see the similarities though.