I have both a Chemistry & Hortoculture background, so the topic of edible/toxic plants intrigues me. A couple of weeks ago, I spent hours studying the difference between Water Hemlock, wild Parsely & wild carrots. At a glance, they all look alike, but the slightest contact with Water Hemlock is fatal.
I am still not comfortable enough to eat other plants that look similar to Water Hemlock (the deadliest plant in North America -- with no known antidote)
Anyhow, the list of toxic plants & their side effects can leave one to choose death by starvation, rather than suffer the alternate consequences of the poisons.
