Aconite aka wolfbane, monkshood. A very small quantity of the root stewed into a tea is enough to cause heart tacycardia. The greeks would dip their arrows in it before battle, but I find no refreance to which bit of the plant but reading through medical literature the root looks the most likely. The toxic princibles are an alkaloid which are more therma stable than the higher alcohol in hemlock waterdropwort.
I should be advailble for the chat room this eveing after 9 pm and I will tell you what I know. Some of it ain't really public domain. I don't know much about lacing darts in the stone age but I know about other later historical applications.
Are asking about poisonous plants on bcuk. Because I can't sign on there at the moment. I have been fansiated by poisonous plant and fungi since my mid teens.