5. Western Water Hemlock
So far it is the most poisonous and deadliest plant of the North America, Western water hemlock grows in wet areas and the odor of this plant is very pleasant. Animals consume the odor of this plant, to show the toxic effect of this plant only a small part is enough.
In some cases, death due to this can happen only in 15 minutes, the effects of this plant starts frothing near the mouth and it get severe as the time passes by. Only some small amount of the plant is lethal.