International Plant Names Index
Standard reference for official plant names, descriptions of families and genera http://www.ipni.org/
C. V. Starr Virtual Herbarium
MBLWHOI Library Digital Herbarium Project
A fully searchable database of specimen images and related data, serving as an online compendium of the marine, freshwater and terrestrial flora of Cape Cod and the Islands. http://mercury.mbl.edu/herbarium/
Index to American Botanical Literature
Online since 1996 and dating back to 1886, this index contains entries dealing with various aspects of extant and fossil American plants and fungi. "America" is defined in the broadest possible sense, encompassing land and marine plants and fungi from Greenland to Antarctica. American territory outside this area, e.g., Hawaii, is not included. http://sciweb.nybg.org/science2/IndexToAmericanBotanicalLiterature.asp
Angiosperms
The focus of this site is on angiosperms, although treatments of gymnosperm groups were added in 2005. Emphasis is placed on plant families because they are the groups - admittedly partly arbitrary as to circumscription, but now for the most part monophyletic - around which many of us organize our understanding of plant diversity. http://www.mobot.org/MOBOT/Research/APweb/welcome.html
Harvard Herbaria
The Harvard University Herbaria, with more than 5 million specimens, are one of the 10 largest Herbaria in the world in number of specimens, and along with the library, form the world's largest university owned herbarium. http://www.huh.harvard.edu/
Botanicus: Botanical Literature
Botanicus is a freely accessible portal to historic botanical literature from the Missouri Botanical Garden Library. Botanicus is made possible through support from the Institute of Museum and Library Services, W.M. Keck Foundation, and the Andrew W. Mellon Foundation. The portal contains >600 book and journal titles, nearly 3,000 volumes, and >1 million pages of information. http://www.botanicus.org/browse/titles | 
