Earth has more than 60,000 known tree species.
Until recently, there was no thorough global census of tree species. But in April 2017, the results of a "huge scientific effort" were published in the Journal of Sustainable Forestry, along with a searchable online archive called GlobalTreeSearch.
The scientists behind this effort compiled data from museums, botanical gardens, agricultural centers and other sources, and concluded there are 60,065 tree species currently known to science. These range from from Abarema abbottii, a vulnerable limestone-bound tree found only in the Dominican Republic, to Zygophyllum kaschgaricum, a rare and poorly understood tree native to China and Kyrgyzstan.
Next up for this area of research is the Global Tree Assessment, which aims to assess the conservation status of all of the world's tree species by 2020.
More than half of all tree species exist only in a single country.
Aside from quantifying the biodiversity of trees, the 2017 census also highlights the need for details about where and how those 60,065 different species live. Nearly 58 percent of all tree species are single-country endemics, the study found, meaning each one naturally occurs only within the borders of a single nation.
Brazil, Colombia and Indonesia have the highest totals for endemic tree species, which makes sense given the overall biodiversity found in their native forests. "The countries with the most country-endemic tree species reflect broader plant diversity trends (Brazil, Australia, China) or islands where isolation has resulted in speciation (Madagascar, Papua New Guinea, Indonesia)," the study's authors write.
Scientists thought this dinosaur-era tree went extinct 150 million years ago — but then it was found growing wild in Australia.
During the Jurassic Period, a genus of cone-bearing evergreen trees now named Wollemia lived on the supercontinent Gondwana. These ancient trees were long known only from the fossil record, and were thought to have been extinct for 150 million years — until 1994, when a few survivors of one species were found living in a temperate rainforest at Australia's Wollemia National Park.
That species, Wollemia nobilis, is often described as a living fossil. Only about 80 mature trees are left, plus some 300 seedlings and juveniles, and the species is listed as critically endangered by the International Union for Conservation of Nature.
While Wollemia nobilis is the last of its genus, there are also still other middle Mesozoic trees alive today. Ginkgo biloba, aka the ginkgo tree, dates back about 200 million years and has been called "the most ancient living tree.