3,000-Year-Old Tree Has a Sex Change

The Fortingall Yew may be thousands of years old, but that doesn't mean it's old-fashioned. In fact, despite having been recorded as male for centuries, this venerable old tree is apparently now getting in touch with its feminine side.

Located in Perthshire, Scotland, the tree is thought to be about 3,000 years old, although some estimates stretch its age as far back as 5,000 years. It's considered the oldest live tree in the U.K., and one of the oldest living things in Europe.

Yews are usually dioecious, meaning each tree is either male or female. The Fortingall Yew has long sported the pollen cones characteristic of male trees, but during a recent visit, Max Coleman of the Royal Botanic Garden Edinburgh (RBGE) discovered three red berries growing from the tree — a telltale sign of a female yew.

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"Males have small spherical structures that release clouds of pollen when they mature," Coleman writes in his blog. "Females hold bright red berries from autumn into winter. It was, therefore, quite a surprise to me to find a group of three ripe red berries on the Fortingall yew this October when the rest of the tree was clearly male."

This is not unheard of, Coleman tells Agence France-Presse, but it's unusual. While certain types of trees often feature male and female parts, yews are typically one or the other. "It's a rare occurrence ... and not fully understood," he says. "It's thought that there's a shift in the balance of hormone-like compounds that will cause this sex change. One of the things that might be triggering it is environmental stress."

Yet the Fortingall Yew appears healthy, he adds — at least as healthy as one can expect from an organism that may predate the Roman Empire. The girth of its trunk was measured at more than 50 feet in 1769, but it has dwindled significantly since then. What's left is largely sapwood, with most of the tree's heartwood having decayed long ago. That makes it difficult to estimate its age, but since trees can survive without any heartwood, it doesn't necessarily indicate illness.

Although a sex change in a 3,000-year-old tree is big news, Coleman points out the Fortingall Yew seems to just be dabbling with the idea so far.

"Normally this switch occurs on part of the crown rather than the entire tree changing sex," he writes. "In the Fortingall Yew, it seems that one small branch in the outer part of the crown has switched and now behaves as female."

It's possible this tree has changed sexes before, Coleman adds, but there's no record of it. "This process may have happened before, but we know the Fortingall Yew has been classed as male for hundreds of years through records," he tells the Guardian. "The sex change isn't the amazing bit in this case; it's the fact it's this particular tree."

The Fortingall Yew's berries were collected for analysis, and Coleman says three of its seeds will be included in a project to conserve yew trees' genetic diversity. The RBGE's existing perimeter hedges will be replaced by a "conservation yew hedge," grown from cuttings and seeds of wild populations as well as certain ancient yews — a genetic resource that will represent more than 2,000 individual trees.

"As it matures, the hedge will display a range of characteristics reflecting the genetic diversity of the many individual trees involved," Coleman writes. "The Fortingall Yew itself will be represented in the hedge and so too, all being well, will its offspring via the curious ability of yew trees to change sex."