A hiker stumbled across some very unusual-looking branches while exploring New York's Catskill Mountains earlier this week, and turned to Reddit to help identify the strange green, crystal-like structures on their exposed ends.
"I’m assuming is a fungus but I thought it was gorgeous!" user Goat-scream11 wrote on the Camping and Hiking subreddit. "I didn’t see any other broken branches that had this greenish blue tint."
Various suggestions were put forward, including bioluminescent mold, blue herbicide, fiberglass and tiberium, but the green coloration was eventually identified as pigment left by the chlorociboria aeruginascens fungus, also known as green elfcup, which grows on wood without bark (like these splintered sticks).
"The green makes a dye or ink that conducts electricity— you can literally draw a circuit board with it," added one poster. "The green v blue apparently depends on the mineral content of the host wood."
Green elfcup produces turquoise, oval-shaped fruiting bodies, but these are less than 3mm long and rarely seen. You are much more likely to spot the coloration left behind by its mycelium (the root-like structure that supports it). The stained wood (particularly oak) is sought after by craftspeople, and is used in decorative woodwork.
According to UK charity The Wildlife Trusts, the wood was in particular demand during the 18th and 19th centuries, when it was used to create delicate inlays for decorative boxes.
"Crafting mosaic patterns from different pieces of stained wood like this was the signature craft of woodworkers who made 'Tonbridge Ware' of Kent," it says.
Green elfcup isn't considered edible, but isn't toxic either. As the Miami Herald reports, the hiker only held the branches for long enough to take a photo, then doused her hands in sanitizer, but it's perfectly safe to hold if you happen to spot some while hiking.
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Cat is the editor of Advnture, She’s been a journalist for 15 years, and was fitness and wellbeing editor on TechRadar before joining the Advnture team in 2022. She’s a UK Athletics qualified run leader, and in her spare time enjoys nothing more than lacing up her shoes and hitting the roads and trails (the muddier, the better), usually wearing at least two sports watches.