In a scene from Shakespeare's Macbeth, a witch's brew is concocted to conjure the souls of the dead. Along with magical animal parts and cursed objects thrown into the cauldron, the witches include plant ingredients: poison hemlock and yew.

Imagine the scene: A cavern with a cauldron in the middle, a thunderstorm booming outside, and three witches chanting: “Double, double toil and trouble; Fire burn, and cauldron bubble.” ~Macbeth, Act IV Scene 1

While we can’t guarantee their ability to connect with the souls of Scottish kings, poison hemlock and yew both have certain nefarious properties that earned them their spot on the witch’s brew ingredient list.

“Root of hemlock digged i' th' dark...” ~Macbeth

Poison hemlock (Conium maculatum) is a hearty, highly poisonous plant in the family Apiaceae. Its tall stems are streaked with purple on the lower half, giving it its Latin name maculatum, meaning “with spots.” It bears clusters of small, white flowers and its leaves emit a foul odor when crushed. A biennial, poisoned hemlock takes two years to complete its life cycle. It is invasive and widely regarded as a noxious weed.

The “poison” in poison hemlock comes from the chemical compounds found within it, specifically coniine. Coniine inhibits the central nervous system, paralyzing to the point of respiratory collapse. It would take an estimated six to eight poison hemlock leaves to kill a grown person, but the roots and seeds can be even more potent. The witches apparently knew this, as their recipe called specifically for the roots!

Make sure you can tell the difference between poison hemlock and Queen Anne's lace; they look similar if you're not looking close enough!

“Gall of goat and slips of yew, Slivered in the moon’s eclipse...” ~Macbeth

The second plant mentioned in the witch’s brew is yew (Taxus baccata), a coniferous tree. Yew trees have short, round trunks that hollow with age. Along with its flat, dark green leaves, this tree produces red seed cones called arils. Yew trees are typically single-sexed, and the males release a highly allergenic pollen that can cause headaches, rashes and difficulty breathing.

All parts of the yew tree are poisonous, with the exception of the fleshy, red fruit of the aril. These should not be consumed, however, as the seed inside is highly toxic. What makes the yew so poisonous is a compound called taxine. Essentially, taxine targets the cardiovascular system. When ingested, taxine can cause increased heart rate, convulsion, respiratory distress and even heart failure. Another sinister quality of yew is that the poison remains after the tree dies. Even if the witches had harvested their “slips of yew” long ago, the poison would be ripe for the conjuring!