London (AFP) - More than 28,000 species of plants around the world have a medical use but poor documentation means people are not making the most of the health benefits, according to a survey released on Thursday.

Britain's Royal Botanic Gardens at Kew in London recorded 28,187 species in its latest annual survey and said it was probably a "very conservative figure".

New plants discovered over the past year include nine species of a climbing vine used in the treatment of Parkinson's disease, the survey found.

"The report is highlighting the huge potential that there is for plants, in areas like diabetes and malaria," said Monique Simmonds, deputy director of science at the world-famous botanical group.

The report said two plants, artemisinin and quinine, are "among the most important weapons" against malaria, which killed over 400,000 people in 2015.

Despite their potential, just 16 percent of the plants Kew recorded as being for medical use are cited in regulatory publications.

Kew's expansive gardens in west London and vast botanic collections, containing over 8.5 million items, are listed as a UNESCO World Heritage site.

The institution's second annual "State of the World's Plants" report involved 128 scientists from 12 countries, who since the first survey have discovered 1,730 new plant species.

They include five new species of Manihot found in Brazil, seven new Aspalathus plants used for making South African rooibos tea, and a new parsnip species uncovered in Turkey.

- Risks from globalisation -

The report also traced the destruction of plants by analysing satellite imagery.

In doing so Kew found that over the past 16 years "an average of around 340 million hectares of the Earth burns every year", which Kew researcher Sarah Wyse likened to the size of India going up in flames annually.

While the figure appears alarming, Wyse said some plants require fire to regenerate.

"These fires are not inherently bad for many ecosystems because most plants adapt to fire," she told AFP.

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Researchers also look at the health of plants, warning the world could face a $540 billion (492 billion euros) annual bill if the spread of invasive pests and pathogens is not stopped.

Kew blamed increased travel and trade in plants for spreading pests and called for stricter biosecurity measures as they are sent around the world.

As well as being costly, the impact can also be deadly, with Kew citing starvation in Africa caused by maize crops decimated by the armyworm.

The director of science at Kew, Kathy Willis, said the broad survey of the current state of affairs should contribute to appreciating and helping plants.

"I hope this will enable us to have a global conversation about what we need to protect and conserve," she said.