Hi,
I usually post in kitchens, and know little about plants, but I need your help.

I am working on my parents' home in Philadelphia, in the aftermath of my father's death, and have come across a plant that I have never seen before. The back yard has been just about invaded with a plant with broad, spade-shaped leaves, and white flowers that eventually turn into purple berries. I grew up in this house, and this plant was definitely not hear years ago.. The plants range in size from 3' high to 8' tall. The stalks are not ligneous, but are rather very soft and watery, kind of like bamboo. (They are stiff on the outside, and pithy on the inside.) The stalks get to maybe 3" in diameter. The root seems like a tap root, which I can pull out in the smaller specimens (but not for larger plants).

Here are some pictures:
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Any ideas appreciated!
Thanks, Angie