This looks like a native perennial, Algeratina altissima.  Commonly known as white snakeroot.  (Previously, this was classified as Eupatorium rugosum.)  

This is a popular native plant, and desirable in the landscape.  It does spread by rhizomes and seed, and where it is very happy it can get aggressive and become a nuisance.  However, it can also be handy to fill in areas and used as a groundcover plant.  

Avoid the variety known as 'Chocolate', which can become downright invasive, and ceases to have the benefits of a native plant.  

If volunteers are a problem, just be sure to prune off the dead flower heads before the seeds can drop.  

ECN