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American Society of Plant Biologists (ASPB)
To promote the growth and development of plant biology, to encourage and publish research in plant biology, and to promote the interests and growth of plant scientists in general
http://www.aspb.org
Botanical Society of the British Isles
Founded in 1836, it is the major source of information on the status and distribution of British and Irish flowering plants and ferns.
http://www.bsbi.org.uk/
