(All these prints are for sale)
I just found a wonderful online site of botanical drawings and paintings from the 17th century to the early 20th century. The majority are of the 19th century, when botanical art (painting) really flourished, as all those adventurous Europeans went to the colonies and beyond to record all the exotic plants they found.
Click to this site, and look on the left side for Botanical Prints, and on the right side for Natural History Prints.