ROME: From London's Kew Gardens to Singapore's Gardens by the Bay, botanic gardens worldwide are home to at least a third of all known plant species - but they need to do more to protect those at risk of extinction, researchers say.

A fifth of plants are currently under threat, but there is no technical reason why any of them should become extinct, scientists said after completing a survey of 1,116 collections.

"The global network of botanic gardens is our best hope for saving some of the world's most endangered plants," said Samuel Brockington of Cambridge University's department of plant sciences, and a curator at the university's botanic garden. "If we do not conserve our plant diversity, humanity will struggle to solve the global challenges of food and fuel security, environmental degradation, and climate change," he said.

In all, the botanic gardens surveyed held more than 105,000 species. "These numbers are all the more remarkable as they represent a minimum estimate, based on data derived from just one-third of botanic gardens worldwide," the researchers wrote in the journal Nature Plants.

Currently, about 10 percent of the storage capacity of botanic gardens is devoted to endangered species, and this needs to be expanded, they said.

Better international coordination is needed to house more species at risk - particularly those from tropical climates, the researchers said.

Most of the world's plants are tropical, and they make up 25 percent of plants in botanic gardens, a large number of which are based in the more temperate climates of Europe and North America.

Substantial investment is needed to build a global system for the conservation of threatened plants that can prevent species extinctions, the researchers wrote.