Key takeaways
- Researchers have documented 64,100 tree species worldwide, with an estimated 9,200 more likely still undiscovered.
- Every tree falls into one of two groups, angiosperms or gymnosperms, a split first drawn in 1825.
- Nearly 30 percent of tree species are threatened with extinction.
Most of us learn to tell trees apart the way we learn faces, by the few features that stick: the needles of a pine, the lobed leaf of an oak, the fan of a palm swaying over a beach. Those details point toward a deeper botanical order that scientists are still mapping. Researchers combining global forest databases have documented 64,100 tree species, and a 2022 study estimated that thereβs roughly 9,200 more species yet to be identified.
"Counting the number of tree species worldwide is like a puzzle with pieces spread all over the world," Jingjing Liang of Purdue University, coordinator of the Global Forest Biodiversity Initiative, said in a University of Michigan release accompanying the study.Β
Those species form forests that cover 4.14 billion hectares, or 32 percent of the planet's land, and they shelter most of Earth's land-based wildlife. Forests provide habitat for 80 percent of amphibian species, 75 percent of bird species, and 68 percent of mammal species, according to the FAO and UN Environment Programme. But Earth has also lost about one-third of its forests since the last ice age, with half of that loss occurring in the 20th century. The first Global Tree Assessment on the IUCN Red List came out in October 2024, and it found at least 16,425 of the 47,282 tree species assessed, or 38 percent, at risk of extinction.Β
The Two Main Types of Trees: Angiosperms and Gymnosperms
Merriam-Webster defines a tree as "a woody perennial plant having a single usually elongated main stem generally with few or no branches on its lower part," a description broad enough to cover a slender ginkgo on a city sidewalk and a sequoia wide enough to dwarf a group of visitors standing at its base.
Every tree belongs to one of two groups: angiosperms or gymnosperms β a division Scottish botanist Robert Brown first described in 1825. Angiosperms develop their seeds inside an enclosed ovary, while gymnosperms carry "naked" seeds on the surface of cones or scales.
Angiosperms
Angiosperms, the flowering plants, include more than 300,000 species and make up about 80 percent of all known green plants. Most broadleaf trees are included here, from oaks and maples to eucalyptus. Older guides often equate the group with deciduous trees, and many temperate species do drop their leaves each fall, though most eucalyptus species stay evergreen year-round.
The group spans a remarkable range of scale. Watermeal, the smallest flowering plant, measures less than 1 millimeter long, while Menara, a yellow meranti in Borneo's Danum Valley, reached 100.8 meters, or about 331 feet, making it likely the tallest flowering plant on Earth. Australia's mountain ash comes close, with Tasmania's Centurion measured at about 96.5 meters.
Gymnosperms
Gymnosperms include most of the familiar evergreens, such as pine, spruce, fir, cedar, and juniper. The majority keep their needles through winter, although some, including ginkgo and dawn redwood, shed their foliage each autumn.
Gymnosperms were the first seed plants and dominated the Mesozoic Era before flowering plants diversified in the Cretaceous and rapidly came to dominate the land flora. Conifers still define the far north, where the boreal forest makes up 29 percent of the world's forest cover and grows mostly across Russia and Canada.
