The Fortingall yew in Perthshire, Scotland, is thought to be anywhere from 2,000 to 5,000 years old and has long been identified as a male tree. Max Coleman with the Royal Botanic Garden of Edinburgh wrote in a blog post last month though that he had observed red berries on the historic tree, indicating that it switched to have some female parts:
Closer examination reveales the Fortingall Yew is a male tree. Yews are normally either male or female and in autumn and winter sexing yews is generally easy. Males have small spherical structures that release clouds of pollen when they mature. 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 Fortingal yew this October when the rest of the tree was clearly male. Odd as it may seem, yews, and many other conifers that have seperate sexes, have been observed to switch sex. Normally this switch occurs on part of the crown rather than the entire tree changing sex. In the Fortingall Yew it seems that one small branch in the outer part of the crown has switched and now behaves as female.Yew trees, specifically the species Taxus baccata, are usually considered dioecious, meaning trees are either male or female only. But under rare circumstances they can become monoicous, having both pollen and egg-bearing structures on one plant.
"It's a rare occurrence ... rare and unusual and not fully understood," Coleman said, according to Agence France-Presse. "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."
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