Encyclopedia of Life (http://eol.org)
Flora Europaea (http://rbg-web2.rbge.org.uk/FE/fe.html)
Global Invasive Species Database (http://www.iucngisd.org/gisd)
Native Species Resolver (http://bien.nceas.ucsb.edu/bien/tools/nsr/nsr-ws/)
Integrated Taxonomic Information Service (http://www.itis.gov/)