Gallery of Connecticut Wildflowers (URL is http://www.ct-botanical-society.org/) Site is from the Connecticut Botanical Society. The color photos of CT wildflowers are accessible by common name, scientific name, or by color group and were obtained from several well-known reference books.
An Illustrated Flora of the Northern United States and Canada by Nathaniel Lord Britton and Addison Brown. In 3 volumes. Dover Publications, Inc., 1970 Main arrangement of information is by family. Line drawings accompany entries. location
Illustrated Guide to Tropical Plants by EJH Corner and K. Watanabe. Hirokawa Publishing Co., Inc., 1969/1983 printing. Line drawings for each entry are found. Numerous drawings in color can also be found in this resource. location
Picture Australia Site is from the National Library of Australia; images are from Australian collections. Follow the Wildflowers trail for drawings, paintings, or photos of Australian wildflowers. Now called Trove.
Wild Flowers of the United States by Harold William Rickett and (Ed.) William C. Steere. McGraw-Hill Book Company, 1966. In 6 volumes, a source for many color drawings of U.S. wild flowers. location