APHIS USDA Noxious Weeds Home Page
http://www.aphis.usda.gov/ppq/weeds
Text of Federal Noxious Weed Act, list of federal noxious weeds, identification characters of selected weeds.

CalFlora
http://www.calflora.org
Calflora provides information on wild California plants for use in conservation, education, and appreciation.

California Native Plant Society
http://www.cnps.org
Notices, articles, projects, membership on all aspects of native plants promotion.

CDFA Encycloweedia http://www.cdfa.ca.gov/phpps/ipc/encycloweedia/encycloweedia_hp.htm
Notes on ID, Biology, & Management of Plants Defined as Noxious Weeds by California Law.