At the time the Earth had significantly higher levels of carbon dioxide in the atmosphere. Botanists say the rise in emissions may have triggered its growth in the past few years.
These plants dominated the planet before the evolution of flowering plants and are now usually found as ornamental plants inside British homes.
"Fifteen, 20 years ago we started growing cycads – it started as an experiment, something you wouldn't normally do," Chris Kidd, curator at Ventnor Botanic Garden, told CNN.
"Fifteen years on, they're not only surviving winters, growing and producing leaves. Five years ago we had a male cycad that produced a cone, and this year we have a male and female both producing cones," he said.