What is the name of this perennial ?

My mystery plant is ~8 ft tall with large multiple flower heads at the top.
It is planted in partial shade and needs a fair amount of water.
It is a perennial, dieing off completely in the fall and coming up from scratch in the spring. Not sure yet how the flower heads finish off and what the seed pods look like.

 

looks like
giant hogweed Heracleum mantegazzianum

watch out it causes photosensitive contact dermatitis

http://images.google.ca/images?q=gi...GB:official&client=firefox-a&um=1&sa=N&tab=wi

http://www.agf.gov.bc.ca/cropprot/weedguid/ghogweed.htm

http://en.wikipedia.org/wiki/Giant_Hogweed

 

Ditto to Pierrot. Nasty invasive weed, get rid of it, but take care! Handle only with thick gloves and clothing, avoid contact with the sap.

 

Sensitivity varies, but if you don't know if you are sensitive you certainly don't want to risk it.

 

Thanks for the info. Its not something I've seen around here. What areas/zones is it commonly seen in?

 

We have enough of it out here that recognition and eradication is promoted. Looks like Pierrot's second link is an example.

Jacobson, Wild Plants of Greater Seattle - Second Edition (2008) deems it "naturalized" and "common."

 

I will definitley be getting rid of it before it goes to seed. Thanks for the info.

 

Useful info on control here (pdf file):
http://www.sl.kvl.dk/upload/kaempe_bjorneklo_eng.pdf