Joyce Kilmer said there's nothing as "lovely as a tree." Those weren't these trees.

1. AN EXPLOSIVE SITUATION

Aptly nicknamed “monkey-no-climb,” the Amazon’s sandbox tree has a trunk covered in sharp spines. The spiky defense comes with a brigade of reinforcements: The tree’s leaves, bark, and sap are all poisonous. Keeping your distance won’t keep you safe, either. When the sandbox’s fruits ripen, they burst open with a loud bang (hence the tree’s other nickname, “dynamite tree”). It can shoot seeds as far as 100 feet with enough force to send you crawling to the doctor.

2. APPLES OF DOOM

The manchineel tree—native to Florida, Central America, Mexico, and the Caribbean—is entirely poisonous, from the sap that oozes from its bark and leaves to its tiny, apple-shaped fruit. The fruits are so dangerous that Spanish explorers called them “little apples of death,” and historians believe that an arrow dipped in manchineel sap killed Spanish conquistador Juan Ponce de León when he arrived in Florida in 1521. You don’t even have to touch this toxic tree to be hurt by it. Water rolling off the leaves can burn your skin, and dripping sap can damage the paint on your car.

3. BOTANY’S ANSWER TO PORCUPINES

The leaves of Australia’s stinging tree are covered with tiny hairs that inject a powerful neurotoxin into the skin of anyone unlucky enough to brush by. The hairs can be impossible to remove and can penetrate protective clothing. Worse, they produce a burn so severe it can trigger heart attacks, and the pain can linger as long as two years. In 1941, a soldier who fell into a tree was in so much agony he had to be tied to his hospital bed for three weeks.