King County's Native Plant Guide
(pictured: swamp rose or clustered wild rose)
Lady Bird Johnson's Wildflower Center at the University of Austin is a site dedicated to cataloguing and describing thousands of wild plants.
Washington Native Plant Society's Native Plant Gallery Index sorts native plants by category or by botanical name.
An example of their many photos is this mountain lady slipper, which blossoms in the deciduous or mixed forests of the Western Cascades to Montana, Alaska and California in June.