Yews are typically dioecious, meaning they are one sex or the other. Male trees have small cones that release clouds of pollen during breeding time, while female trees have bright red berries.
"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," Coleman wrote on the botanic garden's blog.
Conifers such as the yew have been documented as changing sexes, Coleman wrote. But, as he told AFP, the phenomenon is still "a rare occurrence."
Tree sex changes usually happen on a tree's crown, or most of its aboveground parts, rather than the entire tree, Coleman wrote. "In the Fortingall Yew it seems that one small branch in the outer part of the crown has switched and now behaves as female," he added.
The tree, which lives in a small stone enclosure in the Fortingall Churchyard, could be undergoing the transformation as a tactic to prolong its life, Ancient Tree Forum chairman Brian Muelaner told the Guardian.
"The Fortingall Yew is fragmented and it may be so compartmentalized that part of it has become sexually ambiguous," he said. "We are all continuously learning about ancient trees – the aging process of trees is a new science.”
Environmental stress may have triggered the sex change, although the tree appears healthy, Coleman told AFP.
"It's thought that there's a shift in the balance of hormone-like compounds that will cause this sex change," Coleman said.
Explanations aside, this odd behavior will enable botanists aid the Fortingall Yew in producing new offspring; three seeds from the female portion have been harvested and sown at the botanic garden, along with seeds and cuttings from other ancient trees.
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