A global assessment of all 826 known species of eucalypt trees – of which some 812 grow only in Australia – has found almost a quarter are threatened with extinction.

The figures are revealed in the International Union for Conservation of Nature’s update of its “red list” of threatened species.

Eucalypts in their native range of Australia faced threats from human land use, especially agriculture and urbanisation, the IUCN said.

“As keystone species, [eucalypts] define the landscape of the entire Australian continent, and are culturally significant to its First Nations people,” the IUCN said.

Eucalyptus moluccana. Photograph: Harry Rose/Supplied

Some 134 species of eucalypts had drops in numbers of at least 30% and the endangered Rose Mallee had declined by more than half.

Eucalyptus trees are the key food source for koalas. Eucalyptus moluccana was also considered a vulnerable under the new assessment, the IUCN said.

Dr Eve Lucas, a scientist at the UK’s Royal Botanical Gardens at Kew, said: “The completion of the eucalypt assessment is a major milestone for plant conservation: pinpointing and highlighting the hundreds of threatened species in this iconic and ecologically important genus will increase their chances of survival in the face of the uncertain climate of the future.

“Global assessments of large genera of plants are challenging collaborative exercises and critically important to improve our understanding of plant extinction risks and the actions needed to mitigate them.”

Prof David Bowman, who studies the impacts of climate change and fire on trees at the University of Tasmania, told Guardian Australia that while eucalpyts were ubiquitous in Australia, they were also vulnerable.

A Rose Mallee, eucalypt. Photograph: CheongWeei Gan

He said: “I’m not surprised by this assessment. We are talking here about old ecological systems that are being taken to the edge.

“Eucalypts are keystone species and are critical to a huge number of of ecological systems. If you start taking them out, then there will be knock on effects because so many organisms – birds and insects – depend on them. There are a lot of warning signs out there, and this is another one.”

Dr Stuart Blanch, of WWF-Australia, said: “Deforestation and global heating are threatening the survival of eucalypts across Australia.

“It’s not just individual eucalypt species at risk. Entire forest ecosystems dominated by eucalypts are endangered. Some have been cleared down to less than 10% - or even 5% - of their original extent.”

He said that Australia only listed 76 eucalypts as threatened, while IUCN listed 198, which suggested “the federal government should urgently re-assess the plight of these iconic trees”.

He added: “The bushfires have scorched large areas of eucalypts and we hope those forests are still alive and can sprout new leaves.

“There’s hope for eucalypts and other tree species if we take the right action now.”