Patrick R. Roehrdanz/Betty and Gordon Moore Center for Science — Conservation International

Distribution of rare land plants (species with three observations or fewer). Dark blue areas have a proportionally high number of rare species, while areas with relatively low numbers of rare species range from green to yellow.

Biodiversity is a pillar of conservation and a key concern when contending with climate change effects.

Now, research shows the world's rarest land plant species could bear the brunt of climate impacts under representative concentration pathway 8.5, the scenario with the highest greenhouse gas emissions and worst projections of warming and sea level rise.

The paper appears in the journal Science Advances.

Rare plants are surprisingly common.

According to a comprehensive global database, almost 37% of Earth's roughly 435,000 land plant species are rare, meaning people have observed them only five or fewer times. Roughly 28% have three or fewer observations.

"We thought that there would be a lot of rare species, but the sheer number of a very rare species surprised us," said lead author Brian Enquist, professor of ecology and evolutionary biology at the University of Arizona.

Rare plants ought to die out more easily. But researcher found that, like hothouse flowers, they tend to occupy highly stable environments.

Enquist called that fact "disconcerting," because those safe havens lie directly in calamity's path.

"In a time of rapid change, both in terms of land use and climate change, any sort of change in climate appears to be influencing disproportionately these rare species," he said.

Damage to such a large fraction of land plant species could severely harm biodiversity.

In the Americas, rare species tend to cluster in mountainous regions and small, distinct climate regions like the western flank of the Andes and the southern Sierra Madre of Mexico.

Africa's rare land plants collect in South Africa's Cape, the mountains of Madagascar and Cameroon, the Ethiopian highlands and the Somali peninsula.

Southwestern China and Southeast Asia contain rare species hotspots, as do New Guinea and the mountainous strip that runs from Iran through Turkey.

Europe's notable rare plant regions occur in and around the Mediterranean Sea, including the Pyrenees and Caucasus.