Can you name this plant?

[Sea Yacker]

My mom and I are quite curious.  Last summer, a plant sprung up in the
back yard rectangle of her townhouse, not unlike Jacks beanstalk.  By the
end of the summer it was about 6 feet high.  It survived the winter (she
lives in Maryland BTW), in a dormant state and is now about 10 feet high. 
Its trunk or stalk is almost perfectly straight.  It seems like a woody
plant. The "bark" is smooth - almost bamboo like (come to think of it,
could it be bamboo?) - and a dark olive green with many many white spots
all over it.  The leaves are very large (18 inches or so across), and
heart shaped.  There may be a few small branches but as I recall, most of
the leaves are coming directly off the trunk.  The trunk is about an inch
to an inch and a half thick.  It sprung up in an area that was getting a
lot of bird seed, so it may be the product of one of those.  Appreciate
any guesses.

Thanks
-Dave-