>Can anyone suggest a good source for a detailed distribution map of natural
>(or at least well established) populations of _S. purpurea_ west of the
>Mississippi in the Great Plains region? The maps I have aren't all that
>clear on this issue.
Try to check out MCDANIEL (Bull.Tall Timbers Res. Stat. 9:27, 1971).
Although he writes "W to Iowa", his map shows some localities further W in
Minnesota (near Red Lake and ca. 50 km E Moorhead).
WHERRY (Bartonia 15:6, 1933) mentions two localities even further W from
Canada (Alberta: Edmonton; Saskatchewan: Prince Albert) but there seems to
be no specimen of these records. From Minnesota he mentions Pope and Winona
as localities.
Apparently, the species does not (spontaneously) cross the Red River to the
W in the USA. The westernmost records from Canada are rather dubious.
Kind regards
Jan