In a rain forest near Auckland, New Zealand, a leafless kauri tree stump rises a few feet off the ground. These trees can become giants: The country’s biggest, Tāne Mahuta, or the “Lord of the Forest,” has grown 168 feet high, with a 115-foot canopy.

But this stump is just a stump, so unassuming most would pass it by.

One day, two ecologists from Auckland University of Technology spotted it on a hike.

“A normal person would just think it’s dead. It looks dead to a point, but if you look a bit closer, you can see living tissue,” said Sebastian Leuzinger. “We both said to each other, ‘It’s clearly not dead. How does it live?’”

Naturalists have observed living tree stumps in New Jersey, the Sierra Nevadas, British Columbia and elsewhere. But for more than 150 years, how the stumps survived without leaves for photosynthesis was a mystery.