The following resources are available on the open web. Scroll down to see databases of plants, taxonomy, and literature; portal websites with information and links; and some organizations dedicated to the conservation of plants.
Important Notice
Some U.S. federal agencies and initiatives are modifying publicly available data and some datasets may not be accessible on their sites at this time. Look for a notice on visible web pages.
For websites/datasets that appear to be inaccessible, here are two archives you could check:
The following sources link to images and digitized versions of old botanical texts and illustrations of plants. Many images may be restricted due to copyright.
Other resource guides that may be helpful...