Status of Invasive Plants in Washington

Invasive Plants by Category

• Aquatic - 9 species, 781 records
• Conifer Trees - 1 species, 1 records
• Forbs/Herbs - 299 species, 12187 records
• Grass or Grasslike - 76 species, 3273 records
• Hardwood Trees - 45 species, 584 records
• Shrub or Subshrub - 41 species, 1128 records
• Vines - 27 species, 879 records

Top Ten Abundant Invasive Plants (by number of reports)

1. common yarrow - 1587 reports
2. cheatgrass - 495 reports
3. Himalaya blackberry - 403 reports
4. common St. Johnswort - 388 reports
5. Eurasian watermilfoil - 345 reports
6. yellowflag iris - 282 reports
7. foxglove - 248 reports
8. bull thistle - 240 reports
9. Canada thistle - 235 reports
10. purple loosestrife - 201 reports

Top Ten Widespread Invasive Plants (by number of positive counties)

1. Canada thistle - 39/39 (100%)
2. bull thistle - 39/39 (100%)
3. field bindweed - 39/39 (100%)
4. common St. Johnswort - 39/39 (100%)
5. oxeye daisy - 38/39 (97%)
6. reed canarygrass - 38/39 (97%)
7. spotted knapweed - 37/39 (95%)
8. Japanese knotweed - 37/39 (95%)
9. poison-hemlock - 37/39 (95%)
10. diffuse knapweed - 37/39 (95%)

Counties with the most invasive species reported

1. King County - 404 species
2. Klickitat County - 311 species
3. Whitman County - 303 species
4. San Juan County - 287 species
5. Okanogan County - 261 species
6. Walla Walla County - 242 species
7. Pierce County - 240 species
8. Whatcom County - 237 species
9. Spokane County - 234 species
10. Stevens County - 233 species

Counties with the least invasive species reported

1. Douglas County - 88 species
2. Franklin County - 99 species
3. Lincoln County - 114 species
4. Garfield County - 116 species
5. Adams County - 131 species
6. Mason County - 132 species
7. Grant County - 143 species
8. Wahkiakum County - 148 species
9. Grays Harbor County - 154 species
10. Jefferson County - 155 species