Many modern medicines are derived from plants and new uses are being discovered regularly to treat cancers, pain and organ failure, among a host of ailments, Hopper said.
The animal world is also being exploited for food and medicines, but the threat there is no less significant than for plants. Humans shouldn't imagine that the planet and its abundance of life is all theirs for the taking, he said.
"There is that utilitarian argument. But there is also another about our ethical responsibilities. We share this planet with other species. Surely they have a right to exist as much as we do," said Hopper.
"Then there is another aspect that I think is very important to many people. The sheer joy and wonderment of the natural world. It is a bit like walking in the garden here. Most people's shoulders tend to relax a bit and unwind."
Kew is doing its part through the Millennium Seed Bank project, which is well on the way to collecting and storing safely 10 percent of the world's wild plants.
The next goal - as yet a wish without any financial backing - is to raise that total to 25 percent by 2020.
Not only may they be used at some stage in the future to repopulate decimated plant populations in the wild but they might also one day come into their own as sources of new foods, medicines, fuels or even clothes.
Zoos around the world are making similar efforts to conserve members of the animal kingdom through sperm and egg banks.
"I am an optimist," Hopper said. "We may have already lost a lot but we are capable of protecting what is still left out there. But we have to act quickly to stop climate change and end habitat loss. We only have a few decades to make a difference."
"I for one want to leave a living planet for our children."
