'Xylaria polymorpha' is an opportunistic fungus. Image: Stan Tekiela Author / Naturalist / Wildlife Photographer / Getty Images

What’s Halloween without a little fun-gi. Arguably the most creepy of all fungi, Xylaria polymorpha can look like decaying zombie fingers creeping up from the forest floor. Commonly called dead man’s finger fungus , it and other similar sinister-looking fungi in the genus X ylaria grow throughout the United States.

Take a look at at nine creepy pictures of this fungus—if you dare.

Dead man’s fingers are usually spotted at the bottom of decaying or dead trees. They break down deceased wood and release nutrients into the soil so that new plants can grow. Image: NPS/Bradburn.

The finger-like shapes themselves are the fungi’s sexual reproductive structures. Image: Khlongwangchao via Getty Images.

Like a real human finger, their exteriors can be rather stiff and strong. That firmness helps them to release spores and increase their chances of reproducing.…