Focus on Arts and Ecology

How many different types of plants are in the Amazon rain forest? This is an astonishingly hard question to answer. The number is clearly in the range of “really quite a lot,” but scientists have long debated what “a lot” really means. Estimates derived from different types of models range from the tens of thousands to the hundreds of thousands.

In a new report, published in the Proceedings of the National Academy of Sciences, scientists from institutions around the world have come up with a number that represents all plant species that are definitely known to exist in the Amazon rain forest. In total, they report, humans have identified 14,003 species of plants. Most of those plants—52 percent—are shrubs, small trees, lianas, vines, and herbs. The list also includes 6,727 tree species.

To come up with these numbers, the authors of the paper combined research from the entire Amazon basin. They started with checklists from the databases of herbaria and other collections across the world, then verified the plants on the lists, eliminated errors, and updated the identification of species to the current state of knowledge. Creating the list required the work of hundreds of specialists but resulted in a comprehensive accounting of “all currently known seed plant species found in the lowland rain forest biome,” according to the paper.

The researchers took a more restrictive definition of the Amazon rain forest than some estimates of the species diversity there have used. They identified the Amazon as the “lowland rain forest biome” beneath 1,000 meters of elevation, as opposed to the entire Amazon basin, which includes other biomes.

This number—14,003 species of plants—supports the lower end of estimates of Amazonian plant diversity. Even though we certainly don’t know about all the plant species in this part of the world, the number we know of indicates the total is in the tens of thousands.