Harvard researchers discover a new species of hemlock

(Peter Del Tredici/Arold Arboretum)

Researchers have discovered a new species of eastern Asian hemlock, but the tree was growing right in their own arboretum all along.

Former graduate student Nathan Havill was working with senior researcher and botanist Peter Del Tredici in the Arnold Arboretum in Jamaica Plain in the early 2000s when he noticed a hemlock tree did not seem to fit its description.

In a case of mistaken identity, the tree had been labeled as a well-known species of Japanese hemlock. Del Tredici determined the tree was sent to them from Japan and had originated in Korea, thus launching an expedition.

Del Tredici travelled to the South Korean island of Ulleungdo, where he collected about 30 samples of leaves from hemlock trees to compare to the tree back in Boston. The small island is a volcanic haven with a unique ecosystem, home to fishing villages and only accessible by ferry.


“This island has about 30 other species of plants that are essentially endemic – they only grow on this one island,” Del Tredici said. “ It’s a little bit like the Galapagos.”

University of Maine doctoral candidate Garth Holman partnered with Del Tredici on the study, which was published in Systematic Botany in December. Hollman compared the leaf samples Del Tredici collected until he found a match. The pair named the newly discovered tree the Ulleungdo hemlock after the island.

“We postulate that they disappeared from the Korean mainland but they survived on this island,” Del Tredici said. He believes the species grew throughout eastern Asia before the last Ice Age. “[The island] was a lot warmer because it was surrounded by ocean,” he said.

What’s unique about the hemlock is its resistance to a common pest called the hemlock wooly adelgid, which was first noted in the US in the 1950s. Del Tredici said the pest didn’t arrive in Boston until the 1990s, which he attributed to climate change because the bug can not survive in subzero temperatures.


“It’s been spreading steadily throughout eastern North America,” Del Tredici said. “About 60 percent of hemlock is now infested. In most of the areas where it exists, it has killed most of the hemlock trees.”

Del Tredici said it takes about 10 years for the algedids to kill a hemlock, but “it’s pretty lethal.”

Ulleungdo hemlocks could be hybridized with other hemlock breeds to increase resistance to the pest, but Del Tredici said a species that is fully immune to the pests has already been discovered.

“I’ve been unsuccessful to try to convince the nursery industry that they should propagate that and sell it to the general public,” he said. “If the [Ulleungdo hemlock] is going to make any kind of contribution, it’s going to be a long time.”

Del Tredici said because the island of Ulleungdo is already fairly isolated, the tree is naturally somewhat protected. He expects the Korean government to ramp up its protected status, not that’s known to only grow on the island.

To Del Tredici, the discovery isn’t about the island’s significance — it’s about the arboretum.

“People don’t realize just how important a place like that can be and the kinds of contributions it can end up making to science,” he said. “Most people think the arboretum is a place where they go see the lilacs.”

Laney Ruckstuhl can be reached at Follow her on Twitter @laneyruckstuhl.