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The picture was kind of fuzzy so it is hard to tell, but it looks some what like a solidago (goldenrod). Here's a page on one particular type of goldenrod. Give it a look and see if that looks like what you've got.

FataMorgana

Here is a link that might be useful: solidago canadensis

When you say "picked up", do you mean the Park was having a sale and you bought it or that you dug it up?

If they were selling the plant, they should have labelled it or you could call them back and ask.

If you dug the plant without permission -- that's both unethical and illegal.

It is a blurry photo. If not Solidago, maybe a Solidaster? Cross between goldenrod and aster.

--Steve

Here is a link that might be useful: {{gwi:248530}}

It does indeed look like Solidago(Goldenrod)