During a three-year botanical inventory of the Hanford Nuclear Reservation in south-central Washington, we located three previously undescribed entities (Astragalus conjunctus S. Watson var. rickardii Welsh, K.A. Beck, and Caplow, Eriogonum codium Reveal, Caplow, and K.A. Beck, and Physaria douglasii (S. Watson) O'Kane and Al-Shehbaz subsp. tuplashensis (Rollins, K.A. Beck, and Caplow) O'Kane and Al-Shehbaz, four species new to Washington (Cistanthe rosea (S.Watson) Hershk., Gilia leptomeria A. Gray, Loeflingia squarrosa Nutt., and Myosurus clavicaulis M.E. Peck), and one previously described species that had generally gone unnoticed by the American botanical community (Festuca washingtonica E.B. Alexeev). The botanical inventory was a part of the Hanford Biodiversity Project, which was funded by the Department of Energy and administered by The Nature Conservancy of Washington.