The Excluded Taxa list contains 509 taxa that have been have been attributed to Washington, but are not presently considered to be a part of the state's flora by the checklist authors. Taxa may be excluded from the checklist for the following reasons:

• Erroneous reports for the state based on misidentified specimens or a literature error.
• Names used incorrectly (misapplied) in past floras or on herbarium specimens.
• Unverified reports not backed by a voucher specimen or reliable literature reference.
• Garden or crop plants that do not appear to have escaped or become naturalized.

Misapplied are linked to the appropriate accepted name for plants occurring in Washington. Such misapplied names still represent accepted names for taxa that occur outside Washington; as such, they should not be treated as homotypic or heterotypic synonyms. Using these misapplied names to determine accepted names for plants outside Washington should be done with caution.

Boldface font does not indicate native taxa in this list.