Botanical gardens are crucial for the long-term survival of many of the world's plants. A new study, published in Nature Plants, has found that these institutions and collections house at least a third of all known species of plants, including two-fifths of all those classed as “threatened”.

The researchers cross-referenced the working list of all 350,699 known species of plants – although some estimates do put this figure closer to 400,000 – with the records of just one-third of botanical gardens whose species records they could access. They found that the collections were hugely significant, and included at least a third of all named plants species.

Astonishingly, the study finds that these collections cover an impressive range of known species. The 1,116 institutions assessed housed close to 66 percent of all known genera, which is the classification one up from species. And going another rung up the ladder, they also contained an impressive 90 percent of all plant families.

It is thought that of all the plants on this planet, up to 20 percent are in danger of extinction, with many threatened by deforestation, land use changes, and climate change. These managed garden spread around the world, however, are vital to the ongoing survival of many of these species, and house at least 41 percent of all known threatened plants.

But these figures, while outstanding, mask some important gaps in the collections. Species from one of the most ancient plant lineages are vastly underrepresented. As some of the first plants to make the leap from the oceans to the land, non-vascular plants – such as mosses and liverworts – capture a key moment not only in the evolution of plants, but in the history of our planet, and yet only 5 percent of all species are housed in botanical gardens.

There are also significant imbalances in the variety of plants held in these collections. With most of the botanic gardens being located in the Northern hemisphere, it is perhaps not surprising to find that species of plants from temperate environments have much better coverage. They found that around 60 percent of known temperate species are represented in these gardens compared to just 25 percent of tropical species, despite the tropical environment containing the vast majority of plant diversity.

“Currently, an estimated one-fifth of plant diversity is under threat, yet there is no technical reason why any plant species should become extinct. Botanic gardens protect an astonishing amount of plant diversity in cultivation, but we need to respond directly to the extinction crisis,”  explained senior author Dr Samuel Brockington.

“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.”