Pat and JBS,
Myriophyllum heterophyllum is the variable milfoil (or diverse-leaved
milfoil). I was not aware of voucher specimens for this species in Maine
until after the publication of the Flora of Maine. It has, however, been
included in two versions of the addenda, which can be downloaded for free by
visiting http://home.att.net/~arthur.haines and navigating to the products
and services section. There is a link to a free .pdf file that contains the
most recent version of the addenda (which inlcudes errors, species new to
Maine, and new taxonomic concepts). Let me know if you have trouble finding
what you are looking for.
Arthur Haines
Plant Biologist
207-865-4283
Thank you.