European water hemlock (Cicuta virosa) reportedly tastes good*, like parsley, and is also the deadliest plant in all of Northern Europe. The most dangerous part of the plant is the root, but all parts contain cicutoxin, a deadly poison to mammals. Even hemlock roots and parts of them often float around, no need to dig 'em up. Children have died from shockingly small amounts of water hemlock, and a single root can kill a grown man, or a feeding cow (animals get fooled, as well). The plant was traditionally used as a “suicide pill” by some Boreal peoples. Caution adviced, even with a tiny dose.
- The article WhyNot linked mentioned American species of Cicuta spp. and claimed they taste “wrong”. Wouldn’t count on it.