Poison hemlock spreads quickly, causes skin blisters if touched, and can be deadly if ingested — with no known antidote.
Its leaves resemble those of ferns, its stems have purple spots, and it sprouts white flowers. This article explains how to recognize it, and what to do if it’s growing in your yard. The map below shows its current U.S. distribution.
Poison hemlock is “widely distributed” in both eastern and western Washington (see here, p. 10). More info about reporting and dealing with it is on the King County website here.
