[DVF] Den Virtuella floran http://linnaeus.nrm.se/flora/welcome.html; Ett projekt vid Naturhistoriska riksmuseet (Stockholm, Sweden).; Even for non-Swedish speaker, the distribution maps on species are nice (map buttons "Norden" and "Norra halvklotet")
[TFG] Edgar T. Therry, ?1995
The Fern Guide: Northeasten and Midland United States and Adjacent Canada; [Original publication 1961]
[TSF] Eduard Thommen, 1951
Taschenatlas der Schweizer Flora
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Keep in mind that the taxonomic information is copied from various sources, and may include many inaccuracies. Expert help is welcome.