The article mentions that spotted water hemlock is not particularly common, but unfortunately the same cannot be said for poison hemlock. It is a omnipresent weed around here (Pacific Northwest). And it remains poisonous for years after it dies, which makes disposal a problem. This also is a huge issue if it gets into a hay-field. I have heard that some people have tried to burn it, with very poor results.

Also, in this terrible plant family is Cow-Parsnip. https://en.wikipedia.org/wiki/Heracleum_maximum. If touched, it causes your skin to be excessively sensitive to the sun. It is basically reverse-sunscreen.