"The day we lose the last botanic garden is the day the world starts to come to an end, because that's where the knowledge is."
Bellamy warns that for the past 100 years, things have not "looked up", and the world is heading towards the next extinction of many species if the destruction of Mother Nature continues at the current rate.
"This is nothing to do with manmade global warming. It's not the 0.6 degsC rise in temperature, but because we have bulldozed and built chainsaws, and destroyed over one-third of the world's forests. We have lost most of the structure out of most of the ecosystems and their soil. These are all problems."
He continues: "Unless we have botanic gardens that bring all that knowledge together and pass it to other people and the next generation, then I think we are lost."
Bellamy has had a long career as a leading and vocal conservationist and educator. He travels around the world to support conservation projects and lecture on botany and natural history.
He speaks fondly of the Americans, who are building more botanic gardens, and the welcome resurgence of older plant collections around the world thanks in part to growing eco-tourism. However, Bellamy believes more can be done. "Wherever I go, I find people who are sick and tired of seeing the values and the things their parents and grandparents took advantage of disappearing. They want to be part of stitching their patch back into working order."
He adds: "There are tens of thousands of projects all over the world where people say yes, we are part of the problem, but we have to know there is a solution, and then we can become part of that solution."
Botanic gardens offer people hope, explains Bellamy enthusiastically, because plant collections connect people with natural history, such as the University of Bristol's new garden illustrating plant evolution: "There is a huge felled oak tree right across their timeline. This is where people can touch history and say wow. The trees that laid down the horrible fossil fuel that we're all talking about were even bigger than this oak."
He added: "Not only can people touch the oak, but sit on it too, and while they're sat there, think about the potential and problems of fossil fuels."
The challenge facing botanic gardens is now furthering their educational resources for the future, such as school and adult education.
"I'm very glad that people are queuing up to go on courses about gardening, says Bellamy. "They've seen the gardeners off the telly and they actually want to be able to touch plants."
Unfortunately, Bellamy argues, many "naughty" UK universities have sold off their botanic gardens and it's becoming "very difficult" to find an Honours botany degree. "You can't learn botany from books. You have to learn it by touching and growing plants."
Bellamy describes the students at Writhington School, who have award-winning orchids and conservation research, as "brilliant young botanists" who get close to their plants. "They found a niche in their learning and have gone on to infect others," he says.
"It's like the school farms. There are only now 18 schools left that actually farm and that's very important."
Bellamy would like broader education in rural science, something echoed by former prime minister Tony Blair.
"We need rural science teaching at all levels, which would encompass the whole thing, including the proper management of these very diverse islands of ours. I'm very pleased to say that this is happening on an ever-increasing scale."
Before working full-time in the media and public education, Bellamy trained in botany and lectured at Durham University. "I was brought up on (the Royal Botanic Gardens) Kew, living within nine miles of it. I always enjoyed the order beds where you could go, or take your students there, and very quickly get into the swing of how we used to think evolution worked," says Bellamy.
"The Victorians did a fantastic job of setting up gardens and parks in our great towns. They were really saying thank you to either God or Darwin."
In recent years, botanic gardens are recognising new theories of plant classification as gene sequencing continues.
"With all this new stuff," explains Bellamy, "the way of looking at things has changed and I think that is very exciting. I really should now start again at 25 and relearn my botany."
He adds: "I did get a bit cross when I heard that we don't have dicots and monocots anymore, but it has been explained to me and I'm very grateful - although I may have to rewrite every book I've ever written."
1960s and 1982: Senior lecturer at Durham University
1982 to date: Full-time media work with several hundred TV shows and more than 50 books
1997: Stood against John Major for the anti-European Referendum party.