Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
[cite:1286620 ]

Link

All of the nomenclatural, bibliographic, and specimen data accumulated in Missouri Botanical Garden's (MBG) electronic databases during the past 30 years are publicly available here. This system has nearly 1.3 million scientific names and over 4.4 million specimen records.

Great resource for plant distribution beyond US & Canada.
http://www.tropicos.org/