Carol Serr wrote:
This may solve it...  But, apparently there is an introduced species as
well...to confuse things.

http://tncweeds.ucdavis.edu/esadocs/documnts/phraaus.html

"Phragmites australis is found on every continent except Antarctica and
may have the widest distribution of any flowering plant (Tucker 1990).
It is common in and near freshwater, brackish and alkaline wetlands in
the temperate zones world-wide....=20

Because Phragmites has invaded and formed near-monotypic stands in some
North American wetlands only in recent decades there has been some
debate as to whether it is indigenous to this continent or not.
Convincing evidence that it was here long before European contact is now
available from at least two sources. Niering and Warren (1977) found
remains of Phragmites in cores of 3000 year old peat from tidal marshes
in Connecticut. Identifiable Phragmites remains dating from 600 to 900 . . . 
etc., etc.,

Tim T. says: I'll buy that! I must have heard from a doubter, but the 
evidence cited seems most compelling. Thanks Carol. Indeed, it may have been 
recently "locally" invasive -- I believe this is the case in some wetlands 
around the Chesapeake Estuaries -- but obviously widespread on the 
continent.