One-fifth of plants worldwide ‘at risk of extinction’

The analysis came from the Royal Botanic Gardens at Kew, the Natural History Museum and International Union for the Conservation of Nature (IUCN).

Researchers had sampled almost 4,000 species, and concluded that 22% should be classified as "threatened", the same alarming rate as for mammals.

A further 33% of species were too poorly understood to be assessed.

There were an estimated 380,000 plant species in all, and many were victims of habitat loss, such as the clearing of forests for agriculture. Species in tropical rainforests were found to be at greatest risk.

The study, known as the Sampled Red List Index for Plants, was an attempt to provide the most accurate assessment so far.

Previous studies had focused on the most threatened plants or particular regions.

This one instead sampled species from each of the five main groups of plants, and its authors argued that as a result, their conclusions were more credible.

The report came ahead of the UN Biodiversity Conference in Nagoya in Japan next month where ministers were due to discuss why conservation targets kept being missed.