More than half of Australia's unique plants have not been assessed to determine whether they are at risk of extinction, scientists warn.

Conservation experts have gathered in London to provide a snapshot of plant heath and what countries are doing to safeguard hundreds of thousands of species.

The study analyses what individual nations are doing to protect their unique species - those found nowhere else on earth.

Australia's efforts were more on par with low-income countries such as Madagascar, on 42%. "Without comprehensive assessment thousands of unique Australian plant and fungi species could be at risk, and we have no way of knowing which species or where to direct conservation efforts," Gallagher said.

"More than half of the world's plants - 221,399 species - occur in only one country. The countries that are custodians of these unique species have a responsibility to assess if they are at risk and take steps to conserve them if they are."