On the basis that the most hazardous plants are those that look tempting to eat, deadly nightshade Atropa belladonna (top image) tops the list. Its fruits look like ripe cherries, but consuming just five can kill an adult human (though some birds eat them with impunity).
Hemlock water dropwort Oenanthe crocata, a member of the carrot family with swollen roots resembling parsnips and leaves that can be mistaken for celery, contains a toxin that causes rapid death in humans and cattle.
Fool’s parsley Aethusa cynapium has leaves that are similar to culinary parsley and contain the poison found in hemlock. Even picking some plants can be risky
Monkshood Aconitum napellus, a non-native that can occur as a garden escape, is poisonous through skin contact.
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Top image: Getty