The Amazon remains a mystery to botanists, who haven't known how many kinds of trees live in the extremely diverse forests or even what species is most common. Turns out, it's a slender palm called Euterpe precatoria. After counting up tree species from 1170 research sites studied by hundreds of scientists, a team extrapolated the number likely to exist across the entire region. They estimate that Amazonia has about 16,000 species of trees (although they admit the statistical model has some problems, such as not accounting for environmental preferences of various species). Remarkably, half of all the trees belong to only 227 species that dominate in various regions, probably because they resist diseases and herbivores, such as insects. Others may have been planted by humans before Europeans arrived. Many species—11,000—are extremely rare, accounting for a mere 0.12% of trees. Half of these are probably rare enough to be considered globally threatened and may go extinct before they are discovered.