In what is being described as a sign of global warming, an exotic plant in the United Kingdom has produced male and female cones outdoors. This is believed to be the first time this phenomenon took place in 60 million years.

Two plants of cycads, a primitive tree that used to dominate the planet 280 million years ago, have produced cones on the sheltered undercliffs of Ventnor Botanic Garden on the Isle of Wight.

Native to Japan, the species is usually only found indoors as an ornamental plant in Britain. Nevertheless, one of the garden’s plants has produced what is believed to be the first outdoor female cone on record in the UK.

“For the first time in 60m years in the UK we’ve got a male cone and a female cone at the same time,” said Chris Kidd, the curator of Ventnor Botanic Gardens. “It is a strong indicator of climate change being shown, not from empirical evidence from the scientists but by plants”.

Cycads used to live in what is now Britain millions of years ago in an era when the Earth’s climate had naturally high levels of carbon dioxide. Fossils of the plants were found in the Jurassic strata of rock stretching from the Isle of Wight to the Dorset coast.

Seven years ago a plant growing outside at Ventor had produced a male cone. But now different plants have produced flower-like male and females cones, giving botanists the opportunity to transfer pollen and generate a fertilized seed.

Kidd argued that the recent summer’s heatwave and the record-breaking temperatures have caused the plant’s production of cones, with a run of milder winters also helping. Records kept at the botanic garden show that the highest average temperatures for January 100 years ago were lower than today’s lowest average for the same month.

 “It’s not something that’s happened with a short-term mild spell. It’s a longer-term warming which is making these things happen,” he said. “The plant will have made the decision to commit to cone production in summer 2018, and that production is set in place to run through over winter and produce the following year.”

Cycad species are composed of three families, the only surviving members of an ancient and largely extinct lineage that has changed little since the Jurassic period, and so are considered “living fossils”. All cycads are native to warmer parts of the world, but are naturally absent from Europe and Antarctica.